Mobile communication system and communication apparatus

ABSTRACT

In a mobile communication system, a mobile communication apparatus in a vehicle includes a selected resource antenna permitting communication using a selected resource, establishing wireless communication with a target communication apparatus. The mobile communication system includes a propagation path characteristic acquirer section and a resource selector section. The propagation path characteristics acquirer section acquires propagation path characteristics information in association with a future communication position, the propagation path characteristics information being about propagation path characteristics between (i) the target communication apparatus and (ii) a reference antenna equal to the selected resource antenna in antenna characteristics including an antenna format. The resource selector section, based on the propagation path characteristics information, selects a resource to be used in communication at the future communication position before the selected resource antenna of the mobile communication apparatus comes to be placed at the future communication position.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No.2016-19254 filed on Feb. 3, 2016 and Japanese Patent Application No.2016-178771 filed on Sep. 13, 2016, the disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a mobile communication system and to acommunication apparatus included in the mobile communication system.More particularly, the present disclosure relates to a technology forestablishing highly reliable communication.

BACKGROUND

Patent Literature 1: JP 2011-172160 A

In multicarrier communication typically based on the OFDM (OrthogonalFrequency Division Multiplexing) method, a reception apparatusestimates, in some cases, a propagation path based on a received signaland feeds a propagation path estimation result back to a transmissionapparatus as disclosed in Patent Literature 1. Based on the fed-backpropagation path estimation result, the transmission apparatus schedulesresources for communication with the reception apparatus so as to reducepower loss, for instance. This inhibits the quality of communicationfrom being degraded by the influence of a multipath propagation path.

SUMMARY

The influence of a multipath varies with place and frequency. In amobile communication apparatus on a mobile object, a position where thepropagation path estimation result is transmitted is often differentfrom a position where communication is established with a resourceallocated based on the propagation path estimation result. The influenceof the multipath propagation path when the communication is establishedis thus changed from the influence when the propagation path estimationresult was transmitted. Even using the resource determined based on thepropagation path estimation result for communication purposes may notlead to highly reliable communication.

It is an object of the present disclosure to provide a mobilecommunication system and a communication apparatus that are capable ofestablishing highly reliable communication.

To achieve the above object, according to a first example of the presentdisclosure, a mobile communication system is provided as including (i) amobile communication apparatus in a mobile object and (ii) a targetcommunication apparatus that is a target with which the mobilecommunication apparatus communicates. The mobile communication apparatusincludes a selected resource antenna permitting communication using aselected resource and establishes wireless communication using theselected resource antenna. The mobile communication system includes apropagation path characteristics acquirer section and a resourceselector section. The propagation path characteristics acquirer sectionacquires propagation path characteristics information in associationwith a future communication position, the propagation pathcharacteristics information being information about propagation pathcharacteristics between (i) the target communication apparatus and (ii)a reference antenna that is equal to the selected resource antenna inantenna characteristics that includes at least an antenna format. Basedon the propagation path characteristics information acquired by thepropagation path characteristics acquirer section, the resource selectorsection selects in advance a resource used in communication at thefuture communication position between the mobile communication apparatusand the target communication apparatus before the selected resourceantenna of the mobile communication apparatus comes to be placed at thefuture communication position.

The propagation path characteristics acquirer section acquires thepropagation path characteristics information in association with thefuture communication position. The propagation path characteristicsinformation is about the propagation path characteristics between thetarget communication apparatus and the reference antenna having the samecharacteristics as the selected resource antenna. This enables theresource selector section to select a resource for use at the futurecommunication position for the communication between the mobilecommunication apparatus and the target communication apparatus beforethe selected resource antenna of the mobile communication apparatusreaches or is placed at the future communication position. The resourceselected by the resource selector section can be thus used at the futurecommunication position to establish communication, providing highlyreliable communication.

To achieve the above object, according to a second example of thepresent disclosure, a communication apparatus is provided ascommunicating with a mobile communication apparatus used in a mobileobject. The mobile communication apparatus includes a selected resourceantenna permitting communication using a selected resource. Thecommunication apparatus includes a propagation path characteristicsacquirer section and a resource selector section. The propagation pathcharacteristics acquirer section acquires propagation pathcharacteristics information in association with a future communicationposition, the propagation path characteristics information beinginformation about propagation path characteristics between thecommunication apparatus and a reference antenna that is equal to theselected resource antenna in antenna characteristics including at leastan antenna format. Based on the propagation path characteristicsinformation acquired by the propagation path characteristics acquirersection, the resource selector section selects, in advance, a resourceused in communication at the future communication position between themobile communication apparatus and the communication apparatus beforethe selected resource antenna of the mobile communication apparatuscomes to be placed at the future communication position.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagram illustrating a configuration of a mobilecommunication system according to a first embodiment;

FIG. 2 is a block diagram illustrating a configuration of a base stationin FIG. 1;

FIG. 3 is a diagram illustrating a radio wave propagation map;

FIG. 4 is a block diagram illustrating the functions of a controlcircuit in FIG. 2;

FIG. 5 is a block diagram illustrating a configuration of an in-vehicleterminal;

FIG. 6 is a block diagram illustrating the functions of a controlcircuit in FIG. 5;

FIG. 7 is a block diagram illustrating the functions of a controlcircuit in a base station in accordance with a second embodiment;

FIG. 8 is a block diagram illustrating the functions of a controlcircuit in an in-vehicle terminal in accordance with a third embodiment;

FIG. 9 is a diagram illustrating a configuration of a mobilecommunication system according to a fourth embodiment;

FIG. 10 is a block diagram illustrating a configuration of an in-vehicleterminal in FIG. 9;

FIG. 11 is a block diagram illustrating the functions of a controlcircuit in FIG. 10;

FIG. 12 is a block diagram illustrating a configuration of a basestation in FIG. 9;

FIG. 13 is a diagram illustrating how communication is established bythe mobile communication system according to the fourth embodiment;

FIG. 14 is a diagram illustrating propagation path characteristicsinformation determined by a characteristics information determinersection in FIG. 11;

FIG. 15 is a block diagram illustrating the functions of a controlcircuit in the base station in accordance with a fifth embodiment;

FIG. 16 is a diagram illustrating a configuration of a mobilecommunication system according to a sixth embodiment;

FIG. 17 is a block diagram illustrating a configuration of a secondin-vehicle terminal in FIG. 16;

FIG. 18 is a block diagram illustrating the functions of a controlcircuit in FIG. 17;

FIG. 19 is a block diagram illustrating a configuration of a firstin-vehicle terminal in FIG. 16;

FIG. 20 is a block diagram illustrating the functions of a controlcircuit in FIG. 19;

FIG. 21 is a diagram illustrating the propagation path characteristicsinformation determined by a characteristics information determinersection in FIG. 20;

FIG. 22 is a diagram illustrating a configuration of a mobilecommunication system according to a seventh embodiment;

FIG. 23 is a block diagram illustrating a configuration of a firstin-vehicle terminal in FIG. 22;

FIG. 24 is a block diagram illustrating a configuration of a secondin-vehicle terminal in FIG. 22;

FIG. 25 is a block diagram illustrating the functions of a controlcircuit in FIG. 23;

FIG. 26 is a block diagram illustrating the functions of a controlcircuit in FIG. 24;

FIG. 27 is a diagram illustrating the propagation path characteristicsinformation CC determined by the characteristics information determinersection in FIG. 26;

FIG. 28 is a diagram illustrating a configuration of a mobilecommunication system according to an eighth embodiment;

FIG. 29 is a block diagram illustrating a configuration of an in-vehicleterminal in FIG. 28;

FIG. 30 is a diagram illustrating the functions of a control circuit inFIG. 29;

FIG. 31 is a diagram illustrating an allocation example of a frontantenna and a rear antenna allocated by a communication controllersection in FIG. 30;

FIG. 32 is a diagram illustrating another allocation example of a frontantenna and a rear antenna allocated differently from FIG. 31;

FIG. 33 is a block diagram illustrating a configuration of a basestation in FIG. 28.

FIG. 34 is a diagram illustrating the functions of a control circuit inFIG. 33; and

FIG. 35 is a diagram illustrating the relationship between an antennaelement use pattern and an index used by a resource selector section inFIG. 34 to select a spatial resource.

DETAILED DESCRIPTION First Embodiment

Embodiments of the present disclosure will now be described withreference to the accompanying drawings. As in FIG. 1, a mobilecommunication system 100 according to a first embodiment includes a basestation 200 and an in-vehicle terminal 300. The in-vehicle terminal 300corresponds to a mobile communication apparatus.

The base station 200 corresponds to a target communication apparatus ora communication apparatus. The base station 200 is fixed at apredetermined location and used to communicate with the in-vehicleterminal 300. The in-vehicle terminal 300 is mounted in a vehicle 4,that is, a mobile object. Here, the vehicle 4 represents an automobile.In FIG. 1, the vehicle 4, which is traveling on a road 5, is depicted atthree points (i.e., spots) P1, P2, and P3. The vehicle 4 positioned atthese three points indicates that the same vehicle 4 sequentially movesfrom point P1 through point P2 to point P3. Thus, FIG. 1 depicts onlyone vehicle 4. In reality, the in-vehicle terminal 300 is mounted ineach of a plurality of vehicles 4. Additionally, a plurality of basestations 200 may be installed.

[Configuration of Base Station 200]

As in FIG. 2, the base station 200 includes a communicator 210, astorage unit 220, and a control circuit 230. The communicator 210, whichmay be also referred to as a transceiver, includes a transmitter 211, areceiver 212, and an antenna 213. The transmitter 211 modulates andamplifies various signals inputted from the control circuit 230 andtransmits the resulting signals to an outside source through the antenna213. The transmitter 211 according to the first embodiment employs OFDMA(orthogonal frequency-division multiple access) as the access scheme andselects either a phase-shift keying modulation method or a quadratureamplitude modulation method. The receiver 212 demodulates a signalreceived by the antenna 213 and inputs the demodulated signal to thecontrol circuit 230.

The storage unit 220 is writable and stores a radio wave propagation map221 and a road map database 223. The radio wave propagation map 221 is adatabase that stores propagation path characteristics information CCabout various communication positions. The propagation pathcharacteristics information CC indicates propagation pathcharacteristics estimated by OFDM (orthogonal frequency-divisionmultiplexing). The propagation path characteristics information CC,which signifies the frequency characteristics of a propagation path,indicates the characteristics of intensity and phase with respect tofrequency. The propagation path characteristics information CC isillustrated in FIG. 3 as the relationship between frequency andsignal-to-noise ratio at various communication positions. The radio wavepropagation map 221 indicates which frequency exhibits an improvedsignal-to-noise ratio at each communication position. The radio wavepropagation map 221 is created for each model of the in-vehicle terminal300. Note that “information” may be used in the present disclosure notonly uncountable but also countable; information may be equivalent to aninformation item while a plurality of informations may be equivalent toa plurality of information items, for instance.

The radio wave propagation map 221 is created for each model of thein-vehicle terminal 300. This is because antenna characteristics varywith the model of the in-vehicle terminal 300 having an antenna 313. Inthe embodiment, the antenna 313 functions as a reference antenna or as aselected resource antenna. The radio wave propagation map 221 is createdfor each model of the in-vehicle terminal 300; thus, the radio wavepropagation map 221 is created for each model of the antenna 313 of thein-vehicle terminal 300. Further, the antenna 313 functions as thereference antenna; thus, the radio wave propagation map 221 is createdfor each of a plurality of reference antennas. The model of thein-vehicle terminal 300 corresponds to antenna determinationinformation.

As the radio wave propagation map 221 is created for each model of thein-vehicle terminal 300, the radio wave propagation map 221 can becreated based on the propagation path characteristics information CCacquired by antennas having the same antenna characteristics. However,even when the antenna characteristics are not the same, the radio wavepropagation map 221 may be created alternatively based on anotherpropagation path characteristics information CC, which is acquired whencommunicating with the base station 200 by using the reference antennahaving the same antenna characteristics as the selected resourceantenna. Specifically, the antenna characteristics are determined bydirectivity, sensitivity, or features affecting the directivity orsensitivity. For example, an antenna format is one element thatdetermines the antenna characteristics. The term “antenna type” may beused as a substitute for the antenna format. If antennas having the sameantenna format are installed under different conditions, the antennasgenerally have different antenna characteristics. For example, if one ofantennas having the same antenna format is installed on the roof of thevehicle and another antenna is installed in the interior of the vehicle,they do not exhibit the same antenna characteristics because they differin directivity. In addition, the antenna characteristics may include anantenna posture.

Even if the antennas differ in antenna format or in antenna posture,they may be considered to have the same antenna characteristics as faras the antennas are similar in antenna format and antenna posture. Thedegree of similarity by which the antennas may be considered to have thesame antenna characteristics can be set as appropriate depending onrequired accuracy.

The radio wave propagation map 221 includes a reliability index database222. The reliability index database 222 is a database of reliabilityindexes for variety of propagation path characteristics information CCincluded in the radio wave propagation map 221. The reliability indexesindicate the degree of reliability of associated propagation pathcharacteristics information CC. In the embodiment, the reliabilityindexes are determined based on a reproducibility index indicative ofthe degree of reproducibility of the propagation path characteristicsinformation CC.

The reproducibility index is a value indicative of the spread ofdistribution of the propagation path characteristics information CCacquired multiple times at substantially the same communicationposition. The wider the spread of distribution, the lower thereproducibility indicated by the reproducibility index. The degree ofpositional difference by which the communication positions may beconsidered to be substantially the same can be set as appropriatedepending on required accuracy.

Each of the reliability indexes is a value that is obtained bydecreasing the reproducibility index for an error resource upon eachoccurrence of an error. The road map database 223 is a database of roadmaps in digital form.

For instance, in the embodiment, the control circuit 230, which may bealso referred to as an electronic control unit, may be a computer havinga CPU 242, a ROM 250, and a RAM 260. The CPU 242 executes programs inthe ROM 250 or other non-transitory tangible storage medium while usinga temporary storage function of the RAM 260. This enables the controlcircuit 230 to function as various sections in FIG. 4. Further, when thecontrol circuit 230 executes the functions of the various sections,methods corresponding to the programs are executed. Some or all of thefunctions executed by the control circuit 230 may alternatively beimplemented by hardware such as one or more ICs.

[Configuration of Control Circuit 230]

As in FIG. 4, the control circuit 230 includes a map adjuster section231 (which may be also referred to as a map update section or a mapupdate processor section), a position prediction information acquirersection 232, a position predictor section 233, a propagation pathcharacteristics acquirer section 234, a resource selector section 235, acommunication controller section 236, and a reliability adjuster section237. Note that, components such as the resource selector section 235included in a control circuit such as the control circuit 230 each arenamed as being assigned with “section”; however, those components may bealso named, e.g., a resource selector, without being assigned with“section.” This may apply to other embodiments or modifications inaddition to the first embodiment.

First, the map adjuster section 231 will be described. The base station200 periodically transmits a reference signal R to a surrounding area.The reference signal R is a signal for propagation path estimation.Specifically, the reference signal R is a pilot signal whose amplitudeand phase are known or a signal including a pilot signal. The referencesignal R is a known signal allocated to all subchannels. Upon receipt ofthe reference signal R, the in-vehicle terminal 300 determines thepropagation path characteristics information CC based on the receptioncondition of the received reference signal R.

The in-vehicle terminal 300 asynchronously uploads (i) the determinedpropagation path characteristics information CC, (ii) a reference signalreception position that is a position where the reference signal R isreceived, and (iii) the model of the in-vehicle terminal 300, to thebase station 200. When the receiver 212 of the base station 200 receivesthe uploaded information, the map adjuster section 231 acquires thepropagation path characteristics information CC, the reference signalreception position, and the model of the in-vehicle terminal 300, fromthe receiver 212. The map adjuster section 231 then identifies the radiowave propagation map 221 to be updated based on the acquired model, andupdates (i.e., adjusts) the identified radio wave propagation map 221 byusing the propagation path characteristics information CC and thereference signal reception position, which are acquired from thereceiver 212. The update may be performed, for example, by calculating,based on the number of previously acquired propagation pathcharacteristics informations CC, the weighted average of the propagationpath characteristics information CC in the radio wave propagation map221 corresponding to the acquired reference signal reception positionand the acquired propagation path characteristics information CC.

The position prediction information acquirer section 232 will now bedescribed. As described later, the in-vehicle terminal 300 transmitsposition prediction information to the base station 200. The positionprediction information includes the position of the antenna 313 at thetime of position prediction information transmission by the in-vehicleterminal 300 (hereinafter referred to as the uploading-time position),the movement speed of the in-vehicle terminal 300 at the time ofuploading, the ID of the in-vehicle terminal 300, and the model of thein-vehicle terminal. As the position prediction information includes theuploading-time position and the movement speed, the position of theantenna 313 can be predicted after the upload. The position predictioninformation may include the travel direction of the in-vehicle terminal300. However, the travel direction can be predicted based on temporalchanges in the uploading-time position. Further, the travel directioncan be predicted more accurately when a road extension direction is usedin addition to the temporal changes in the uploading-time position.Therefore, the position prediction information need not always includethe travel direction. The position prediction information is received bythe receiver 212 of the base station 200. The position predictioninformation acquirer section 232 acquires the position predictioninformation from the receiver 212.

Based on the position prediction information acquired by the positionprediction information acquirer section 232, the position predictorsection 233 successively determines a future predicted position of theantenna 313 of the in-vehicle terminal 300. Specifically, from themovement speed of the in-vehicle terminal 300, which is included in theposition prediction information, and the elapsed time from the time ofposition prediction information reception, the position predictorsection 233 calculates the distance that is moved by the in-vehicleterminal 300 from the time of position prediction information update bythe in-vehicle terminal 300. The predicted position is a position thatis obtained when the uploading-time position is moved in the movementdirection of the in-vehicle terminal 300 by the moved distance. Themovement direction of the in-vehicle terminal 300 may be determinedbased on a track moved by the in-vehicle terminal 300, which isdetermined from the position prediction information successivelyacquired from the same in-vehicle terminal 300. If the positionprediction information includes the travel direction of the in-vehicleterminal 300, the travel direction may be regarded as the movementdirection of the in-vehicle terminal 300.

The propagation path characteristics acquirer section 234 regards thepredicted position predicted by the position predictor section 233 as acommunication position (i.e., a future communication position), andacquires the propagation path characteristics information CC about thecommunication position from the radio wave propagation map 221 inassociation with the communication position. The position predictioninformation includes the model of the in-vehicle terminal 300, and theradio wave propagation map 221 is created for each model of thein-vehicle terminal 300. Therefore, the radio wave propagation map 221from which the propagation path characteristics information CC isacquired is the same radio wave propagation map 221 as for the model ofthe in-vehicle terminal 300 that is included in the position predictioninformation. FIG. 3 indicates, as an example, the propagation pathcharacteristics information CC (P2), which is acquired from the radiowave propagation map 221 when point P2 is a predicted position, by usinga combination of solid line and dotted line along the solid line.

Based on the propagation path characteristics information CC acquired bythe propagation path characteristics acquirer section 234, the resourceselector section 235 selects a resource that is to be used forcommunicating with the in-vehicle terminal 300 at the predicted position(i.e., a future communication position) predicted by the positionpredictor section 233. For example, as in FIG. 3, the propagation pathcharacteristics information CC (P2) indicates that the signal-to-noiseratio is high between frequency f1 and frequency f2. Therefore, asubcarrier using a frequency between frequencies f1 and f2 is selectedas a frequency resource to be used for communicating with the in-vehicleterminal 300 in a time slot including a time at which the in-vehicleterminal 300 is placed at the communication position. This results inthe selection of a frequency resource in a certain time slot (i.e., atime resource).

A reliability index corresponding to the propagation pathcharacteristics information CC is also used to select a resource. Afrequency resource having a relatively low reliability index is selectedwith the signal-to-noise ratio corrected to a relatively small value incoordination with low reliability.

The above explanation applies to a case acquiring the propagation pathcharacteristics information CC for one in-vehicle terminal 300. Incontrast, acquiring the propagation path characteristics information CCfor a plurality of in-vehicle terminals 300 needs to optimize a resourceallocation.

Such optimization is to maximize the total or average amount of time andfrequency resource that keeps radio attenuation for one or morein-vehicle terminals 300 not higher than a predetermined level (i.e.,keeps the signal-to-noise ratio not lower than a predetermined level).The method of selecting a frequency resource based on acquiredpropagation path characteristics may be the same as the method used inan existing system such as an LTE cellular system.

The resource selector section 235 selects a resource for use incommunication with the in-vehicle terminal 300 at a predicted position,that is, at a position still not reached by the in-vehicle terminal 300.This allows the resource to be selected before the antenna 313 of thein-vehicle terminal 300 reaches the predicted position, i.e., comes tobe placed at the predicted position (i.e., the future communicationposition).

While successively determining the position of the in-vehicle terminal300 based on the position prediction information, the communicationcontroller section 236 uses the resource selected by the resourceselector section 235 as the resource for the determined position andcontrols the transmitter 211 to perform a communication with thein-vehicle terminal 300.

Such communication may adopt a modulation method of either a phase-shiftkeying modulation or a quadrature amplitude modulation asmentioned-above for the transmitter 211. The phase-shift keyingmodulation may select BPSK or QPSK; the quadrature amplitude modulationmay select 16 QAM, 64 QAM, or 256 QAM. BPSK, QPSK, 16 QAM, 64 QAM, and256 QAM are such that communication speed and reliability arecontradictory to each other. Specifically, the higher the communicationspeed, the lower the reliability. Therefore, the reliability of aselected resource is determined according to the signal-to-noise ratio;a modulation method providing a relatively high communication speed isselected when the reliability is relatively high. Namely, a modulationmethod providing a relatively low communication speed is selected whenthe reliability is relatively low. Further, relatively high redundancymay be employed (i.e., a relatively low code rate may be employed) whenthe reliability is relatively low. In FIG. 1, the base station 200transmits a signal to the in-vehicle terminal 300 by using a selectedfrequency resource when the vehicle 4 is positioned at point P2.

The above communication controller section 236 applies to a downlink,but may also apply to an uplink communicating with the in-vehicleterminal 300 by using a resource selected by the resource selectorsection 235.

When a resource selected by the resource selector section 235 is usedfor an uplink, the communication controller section 236 should transmita signal indicative of the resource selected by the resource selectorsection 235 to the in-vehicle terminal 300 before the in-vehicleterminal 300 reaches the communication position.

Upon receipt of the signal transmitted from the base station 200, thein-vehicle terminal 300 checks for an error in the signal. Errorresource information including an error resource and the currentposition of the antenna 313 is then uploaded to the base station 200.

When the receiver 212 of the base station 200 receives the errorresource information, the reliability adjuster section 237 acquires theerror resource information from the receiver 212. Then, based on theacquired error resource information, the reliability index for thecommunication position and frequency resource determined by the errorresource information, which is among the reliability indexes in thereliability index database 222, is lowered by a predetermined amount orby a predetermined percentage.

[Configuration of in-Vehicle Terminal 300]

As in FIG. 5, the in-vehicle terminal 300 includes a communicator 310, astorage unit 320, and a control circuit 330. The communicator 310, whichmay be also referred to as a transceiver, includes a transmitter 311, areceiver 312, and the antenna 313. The transmitter 311 modulates andamplifies various signals inputted from the control circuit 330 andtransmits the resulting signals to an outside source through the antenna313. The transmitter 311 according to the embodiment employs SC-FDMA asthe access scheme and selects either a phase-shift keying modulationmethod or a quadrature amplitude modulation method. The receiver 312demodulates a signal received by the antenna 313 and inputs thedemodulated signal to the control circuit 330. As mentioned, the antenna313 functions as the reference antenna and as the selected resourceantenna. Various information can be written into the storage unit 320,which is controlled by the control circuit 330.

For instance, in the embodiment, the control circuit 330, which may bealso referred to as an electronic control unit, may be a computer havinga CPU 342, a ROM 350, and a RAM 360. The CPU 342 executes programsstored in the ROM 350 or other non-transitory tangible storage mediumwhile using a temporary storage function of the RAM 360. This enablesthe control circuit 330 to function as various sections in FIG. 6.Further, when the control circuit 330 executes the functions of thevarious sections, methods corresponding to the programs are executed.Some or all of the functions executed by the control circuit 330 mayalternatively be implemented by hardware such as one or more ICs.

A speed sensor 41 successively detects the movement speed of thein-vehicle terminal 300 and inputs the detected movement speed to thecontrol circuit 330. A vehicle speed sensor detecting the speed of thevehicle 4 may be used as the speed sensor 41.

A position detector 42 includes a GNSS (Global Navigation SatelliteSystem) receiver that receives a navigation signal transmitted from anavigation satellite included in a GNSS. The position detector 42successively detects the current position based on the navigation signalreceived by the GNSS receiver. The detected current position is thensuccessively inputted to the control circuit 330.

[Configuration of Control Circuit 330]

As in FIG. 6, the control circuit 330 includes a position determinersection 331, a communication controller section 332, an error detectorsection 338, and a characteristics information determiner section 339.Note that, components such as the characteristics information determinersection 339 included in a control circuit such as the control circuit330 each are named as being assigned with “section”; however, thosecomponents may be also named, e.g., a characteristics informationdeterminer, without being assigned with “section.” This may apply toother embodiments or modifications in addition to the first embodiment.

The position determiner section 331 successively determines the currentposition of the antenna 313 by successively acquiring the currentposition detected by the position detector 42. The current positiondetected by the position detector 42 is the position where the positiondetector 42 is disposed, and is not the current position of the antenna313. Therefore, the current position detected by the position detector42 may be corrected based on the difference between the position of theantenna 313 and the position of the position detector 42 to use thecorrected current position as the current position of the antenna 313.In the embodiment, the antenna 313 functions as the reference antennaand as the selected resource antenna. Therefore, even if the position ofthe position detector 42 is the position of the reference antenna andthe position of the selected resource antenna, it does not affect theaccuracy with which the selected resource antenna is determined to beplaced at the position of the reference antenna. If the position errorof the reference antenna is equal to the position error of the selectedresource antenna, it is not necessary to correct the current positiondetected by the position detector 42 and use the corrected currentposition as the current position of the antenna 313.

The communication controller section 332 includes a reception controllersection 333 and a transmission controller section 334. The receptioncontroller section 333 decrypts a signal for a resource block allocatedto the local terminal (i.e., the in-vehicle terminal 300 itself), amongsignals that are transmitted from the base station 200 and received bythe antenna 313. What resource is allocated to the local terminal isdetermined by a method preselected for each wireless system. In the LTEcellular system, for example, the determination is made based onallocation information in a control channel area of each wireless frame.The antenna 313 is used to receive a signal of a resource selected bythe resource selector section 235 of the base station 200. Thus, theantenna 313 corresponds to the selected resource antenna.

Before the transmission controller section 334, the error detectorsection 338 and the characteristics information determiner section 339will be described. The error detector section 338 uses a well-knownerror detection method based on an error-correcting code to check for anerror in a signal that is transmitted by using a resource allocated tothe local terminal.

When the receiver 312 receives the reference signal R from the basestation 200, the characteristics information determiner section 339acquires the reference signal R from the receiver 312 and determines thepropagation path characteristics information CC on the receptioncondition of the received reference signal R. The method of estimatingthe propagation path characteristics information CC based on thereceived reference signal R may be the same as a method widely used, forexample, for MIMO. The propagation path characteristics information CCis also referred to as a propagation path state or a propagation pathestimation result. The propagation path characteristics information CCis expressed by frequency-specific power and phase.

The transmission controller section 334 includes a characteristicsdetermination information uploader section 335, a position predictioninformation uploader section 336, and an error resource uploader section337. The characteristics determination information uploader section 335uploads (i) the position (i.e., received position) where the referencesignal R is received, (ii) the propagation path characteristicsinformation CC determined by the characteristics information determinersection 339, and (iii) the model of the in-vehicle terminal 300, fromthe transmitter 311 to the base station 200. The time of uploading isnot limited to the time of determining the propagation pathcharacteristics information CC, that is, the upload may be performedasynchronously. In FIG. 1, the in-vehicle terminal 300 uploads thepropagation path characteristics information CC at a time when thevehicle 4 is positioned at point P1.

As mentioned, the propagation path characteristics information CCuploaded by the characteristics determination information uploadersection 335 is used when the map adjuster section 231 of the controlcircuit 230 in the base station 200 updates the radio wave propagationmap 221. Therefore, the antenna 313 functions as the reference antenna.

The position prediction information uploader section 336 successivelyuploads the aforementioned position prediction information to the basestation 200. As mentioned, the position prediction information includes(i) the uploading-time position that is the position of the antenna 313at the time of position prediction information transmission from thein-vehicle terminal 300, (ii) the movement speed of the in-vehicleterminal 300 at the time of uploading, (iii) the ID of the in-vehicleterminal 300, and (iv) the model of the in-vehicle terminal 300.

The error resource uploader section 337 uploads, to the base station200, error resource information indicative of a resource used for thetransmission of a signal in which an error is detected by the errordetector section 338. The error resource information includes (i) thefrequency resource in which an error occurred and (ii) the positionwhere the error occurred.

The upload of the error resource information may be asynchronouslytimed. In FIG. 1, the in-vehicle terminal 300 uploads the error resourceinformation about an error detected at point P2 when the vehicle 4 ispositioned at point P3.

[Summary of First Embodiment]

In the first embodiment, the base station 200 includes the propagationpath characteristics acquirer section 234; the propagation pathcharacteristics acquirer section 234 acquires the propagation pathcharacteristics information CC, which was obtained when the antenna 313previously communicated with the base station 200, from the radio wavepropagation map 221, in association with a predicted position (i.e., afuture communication position).

When the propagation path characteristics information CC is acquired inassociation with the future communication position, the resourceselector section 235 can select a resource to be used when thein-vehicle terminal 300 communicates with the base station 200 at thecommunication position before the antenna 313 of the in-vehicle terminal300 comes to be placed at the communication position (i.e., beforereaching the communication position). Thus, the resource selected by theresource selector section 235 can be used at the communication positionto establish communication with high reliability.

Second Embodiment

A second embodiment will now be described. In the second and subsequentembodiments, elements designated by the same reference numerals as thepreviously used ones are identical with the elements designated by thesame reference numerals unless specifically stated otherwise. Further,when only part of configuration is described, previously describedembodiments can be applied to the other part thereof.

As in FIG. 7, the control circuit 230 according to the second embodimentincludes a distance determiner section 238, a characteristics changedeterminer section 239, and a characteristics change compensator section240, in addition to the sections included in the first embodiment.

The distance determiner section 238 acquires the movement speed of thein-vehicle terminal 300, which is included in the position predictioninformation, from the receiver 212 that received the position predictioninformation. The distance moved during one communication period isdetermined by multiplying the movement speed by a predefinedcommunication time per communication.

The characteristics change determiner section 239 determines thecommunication position for the start of communication based on theresult of prediction by the position predictor section 233. Further, thecharacteristics change determiner section 239 determines thecommunication position for the end of communication by adding thedistance moved during one communication period, which is determined bythe distance determiner section 238, to the communication position forthe start of communication. The characteristics change determinersection 239 then acquires from the radio wave propagation map 221 (i)the propagation path characteristics information CC about thecommunication position for the start of communication and (ii) thepropagation path characteristics information CC about the communicationposition for the end of communication.

Next, the ratio of the propagation path characteristics information CCabout the communication position for the end of communication to thepropagation path characteristics information CC about the communicationposition for the start of communication is regarded as a change in thepropagation path characteristics information CC during the communicationperiod.

The characteristics change compensator section 240 compensates for acommunication signal so as to reduce the influence exerted uponcommunication by the change in the propagation path characteristicsinformation CC during the communication period, the change beingdetermined by the characteristics change determiner section 239. Thecommunication signal is either an outgoing signal or an incoming signal.The radio wave propagation map 221 is necessary for making the abovecompensation. Therefore, the communication signal is an outgoing signalif a transmitting end has the radio wave propagation map 221, and is anincoming signal if a receiving end has the radio wave propagation map221.

In the second embodiment, the base station 200 includes the radio wavepropagation map 221. Therefore, when the base station 200 transmits asignal, the signal transmitted from the base station 200 is compensatedfor, and when the base station 200 receives a signal, the signalreceived by the base station 200 is compensated for.

If it is determined by the characteristics change determiner section 239that, for example, the signal-to-noise ratio at the start oftransmission is reduced to half at the end of transmission, thecompensation is made so that transmission power used at the end oftransmission is two times as great as the transmission power used at thestart of transmission. Further, if it is determined by thecharacteristics change determiner section 239 that a phase angle at thestart of transmission advances by 90 degrees at the end of transmission,the phase angle of a signal at the end of transmission is delayed by 90degrees from the phase angle at the start of transmission. Thetransmission power and phase angle between the start and end oftransmission may be determined by interpolation.

Another example may compensate an uplink, i.e., a signal transmittedfrom the in-vehicle terminal 300. When an uplink signal is compensatedfor, the power and phase angle are compensated for before demodulating asignal received by the antenna 213.

Further, if having the radio wave propagation map 221 by downloading itfrom the base station 200, the in-vehicle terminal 300 may include thedistance determiner section 238, the characteristics change determinersection 239, and the characteristics change compensator section 240.

Thus the second embodiment compares the propagation path characteristicsinformation CC about the start of communication and the propagation pathcharacteristics information CC about the end of communication with eachother, and makes compensation so as to reduce the influence of a changein the propagation path characteristics information CC uponcommunication, further improving the reliability of communication.

Third Embodiment

In a third embodiment, the in-vehicle terminal 300 downloads the radiowave propagation map 221 stored in the storage unit 220 of the basestation 200 and stores the downloaded radio wave propagation map 221 inthe storage unit 320. In the third embodiment, the storage unit 320corresponds to a download data storage unit.

The radio wave propagation map 221 stored in the storage unit 320 may beexactly the same as the radio wave propagation map 221 stored in thestorage unit 220 of the base station 200. Alternatively, the radio wavepropagation map 221 stored in the storage unit 320 may be limited tomerely show an area around the current position.

As in FIG. 8, the control circuit 330 of the in-vehicle terminal 300according to the third embodiment includes a difference determinersection 340 in addition to the sections included in the firstembodiment.

The difference determiner section 340 determines a propagation pathcharacteristics difference. The propagation path characteristicsdifference is a difference between the propagation path characteristicsinformation CC determined by the characteristics information determinersection 339 and a portion of the radio wave propagation map 221 storedin the storage unit 320 that corresponds to the propagation pathcharacteristics information CC determined by the characteristicsinformation determiner section 339. The propagation path characteristicsdifference may be determined in units of one propagation pathcharacteristics information CC about each communication position or maybe determined by dividing one propagation path characteristicsinformation CC about each communication position into a plurality offrequency bands and comparing them.

The characteristics determination information uploader section 335 inthe third embodiment uploads the propagation path characteristicsdifference determined by the difference determiner section 340 ascharacteristics determination information. This reduces the amount ofdata to upload, inhibiting a communication band from being compressed.

Fourth Embodiment

As in FIG. 9, a mobile communication system 1000 according to a fourthembodiment includes a base station 1200 and an in-vehicle terminal 1300.The base station 1200 corresponds to the target communication apparatus;the in-vehicle terminal 1300 corresponds to the mobile communicationapparatus. The mobile communication system 1000 may include a pluralityof base stations 1200 and a plurality of in-vehicle terminals 1300.

[Configuration of in-Vehicle Terminal 1300]

As in FIG. 9, the in-vehicle terminal 1300 includes a front antenna 1371and a rear antenna 1372. These antennas 1371, 1372 are equal instructure, mounted on the roof of the vehicle 4 with a front-rearpositional relation (i.e., longitudinally disposed in the traveldirection of the vehicle 4), and positioned at the same height. Thefront antenna 1371 functions as the reference antenna; the rear antenna1372 functions as the selected resource antenna.

As in FIG. 10, the in-vehicle terminal 1300 includes a communicator1310, a storage unit 1320, and a control circuit 1330. The communicator1310 includes a transmitter 1311 and a receiver 1312. The transmitter1311 and the receiver 1312 selectively use the two antennas 1371, 1372for transmission and reception. The transmitter 1311 and the receiver1312 have the same functions as the transmitter 311 and receiver 312 inthe first embodiment, but additionally have a function of switchingbetween the antennas.

As in FIG. 11, the control circuit 1330 includes, as its functions, acharacteristics information determiner section 1331 and a receptioninformation transmitter section 1332. First, the characteristicsinformation determiner section 1331 will be described. In the fourthembodiment, too, the base station 1200 periodically transmits thereference signal R. Both the front antenna 1371 and the rear antenna1372 can receive the reference signal R.

The characteristics information determiner section 1331 acquires fromthe receiver 1312 the reference signal R received by the front antenna1371 or the rear antenna 1372, and determines the propagation pathcharacteristics information CC in the same manner as the characteristicsinformation determiner section 339 according to the first embodiment.The propagation path characteristics information CC determined from thereference signal R received by the front antenna 1371 is hereinafterreferred to as the front antenna propagation path characteristicsinformation CCA; the propagation path characteristics information CCdetermined from the reference signal R received by the rear antenna 1372is hereinafter referred to as the rear antenna propagation pathcharacteristics information CCB.

The reception information transmitter section 1332 uses the transmitter1311 to transmit the followings to the base station 1200: the frontantenna propagation path characteristics information CCA and rearantenna propagation path characteristics information CCB determined bythe characteristics information determiner section 1331; the movementspeed of the in-vehicle terminal 1300 at the time of reception of thereference signal R; the distance between the front antenna 1371 and therear antenna 1372; and the ID of the in-vehicle terminal 1300.

[Configuration of Base Station 1200]

The base station 1200 has the same hardware configuration as the basestation 200 in the first embodiment. Specifically, the base station 1200includes the same hardware as the base station 200 according to thefirst embodiment, namely, a communicator 1210, a storage unit 1220, anda control circuit 1230, as in FIG. 12. Thus, a transmitter 1211, areceiver 1212, and an antenna 1213, which are included in thecommunicator 1210, are identical with the transmitter 211, receiver 212,and antenna 213 included in the communicator 210 in FIG. 2.

The control circuit 1230 differs in functionality from the controlcircuit 230 in FIG. 2. As in FIG. 12, the control circuit 1230 includes,as its functions, a propagation path characteristics acquirer section1231, a resource selector section 1232, a timing determiner section1233, and a communication controller section 1234.

The propagation path characteristics acquirer section 1231 acquires fromthe receiver 1212 the front antenna propagation path characteristicsinformation CCA and rear antenna propagation path characteristicsinformation CCB that are transmitted from the reception informationtransmitter section 1332 of the in-vehicle terminal 1300 and received bythe receiver 1212. Such information is supposed to be received when thein-vehicle terminal 1300 is at a reception position (i.e., at acommunication position). Namely, the front antenna propagation pathcharacteristics information CCA and the rear antenna propagation pathcharacteristics information CCB are associated with the position wherethe information is received.

The resource selector section 1232 regards the position where thereference signal R is received by the front antenna 1371 as thecommunication position, and determines the resource to be used forcommunication at the communication position based on the front antennapropagation path characteristics information CCA acquired by thepropagation path characteristics acquirer section 1231.

The resource selector section 1232 further determines the resource for arear time post-period. The rear time post-period is a period that issubsequent to a rear communication time determined by the timingdeterminer section 1233 and is a predicted period of time required forthe rear antenna 1372 to reach the position of the front antenna 1371 atthe rear communication time.

The movement speed of the in-vehicle terminal 1300 is used to determinethe rear communication time. The time of transmission of the referencesignal R corresponding to the front antenna propagation pathcharacteristics information CCA acquired together with the movementspeed is referred to as the front communication time. The frontcommunication time is time t1 in FIGS. 13 and 14. The rear communicationtime is time t2 in FIGS. 13 and 14. An example of the rear timepost-period is time t3 in FIGS. 13 and 14.

During the rear time post-period, it can be estimated that thepropagation path characteristics information CC is between the frontantenna propagation path characteristics information CCA acquired by thepropagation path characteristics acquirer section 1231 at the frontcommunication time and the front antenna propagation pathcharacteristics information CCA acquired by the propagation pathcharacteristics acquirer section 1231 at the rear communication time.The resource for the rear time post-period is determined based on theestimable propagation path characteristics information CC.

Based on the movement speed of the in-vehicle terminal 1300, which isreceived by the receiver 1212, the timing determiner section 1233determines the time at which the rear antenna 1372 is placed at theposition where the reference signal R is received by the front antenna1371 (i.e., the aforementioned communication position). The determinedtime is the aforementioned rear communication time.

The communication controller section 1234 periodically transmits theaforementioned reference signal R from the transmitter 211. Further, atthe rear communication time determined by the timing determiner section1233, the communication controller section 1234 communicates with thein-vehicle terminal 1300 by using the resource that is selected by theresource selector section 1232 as the resource for use at the rearcommunication time. The communication here is, specifically, atransmission so that a predetermined signal is transmitted by using theselected resource. Furthermore, in addition to the predetermined signal,the reference signal R is transmitted by using all the subchannels. Thecommunication controller section 1234 corresponds to a target apparatuscommunication controller section.

Moreover, during the rear time post-period, the communication controllersection 1234 communicates with the in-vehicle terminal 1300 by using theresource that is selected by the resource selector section 1232 as theresource for use during the rear time post-period.

[Exemplary Communication in Fourth Embodiment]

At time t1 in FIG. 13 (A), the base station 1200 transmits the referencesignal R (t1), and the in-vehicle terminal 1300 receives that referencesignal R (t1). After time t1, the characteristics information determinersection 1331 of the in-vehicle terminal 1300 acquires the referencesignal R (t1) received by the front antenna 1371 and determines thefront antenna propagation path characteristics information CCA. Next,before time t2, the reception information transmitter section 1332transmits the front antenna propagation path characteristics informationCCA, the movement speed, and the ID of the in-vehicle terminal 1300 tothe base station 1200. The propagation path characteristics acquirersection 1231 of the base station 1200 acquires these informations, suchas the front antenna propagation path characteristics information CCA,from the receiver 1212.

FIG. 14 (A) illustrates the front antenna propagation pathcharacteristics information CCA that is acquired by the propagation pathcharacteristics acquirer section 1231 in the state in FIG. 13 (A). Thefront antenna propagation path characteristics information CCA in FIG.14 (A) is depicted with the horizontal axis representing the frequencyand the vertical axis representing the signal-to-noise ratio. The frontantenna propagation path characteristics information CCA in FIG. 14 (A)exhibits the signal-to-noise ratio varying with the frequency.

Thus the resource selector section 1232 of the base station 1200 selectsa frequency channel having a good signal-to-noise ratio as the resourcefor use at the communication position. In FIG. 14 (A), frequenciesf3-f4, f5-f6, and f7-f8 form frequency bands having a goodsignal-to-noise ratio; the resource selector section 1232 selects afrequency channel using such frequency bands as the resource for use atthe communication position.

The timing determiner section 1233 determines the rear communicationtime based on the movement speed of the in-vehicle terminal 1300. Therear communication time is the time at which the rear antenna 1372 isplaced at the communication position of the front antenna 1371. The rearcommunication time is determined by adding the time calculated bydividing the distance between the front antenna 1371 and the rearantenna 1372 by the movement speed of the in-vehicle terminal 1300 tothe time of transmission of the reference signal R corresponding to thefront antenna propagation path characteristics information CCA.

At the rear communication time, the base station 1200 communicates withthe in-vehicle terminal 1300. Time t2 in FIG. 14 (B) is the rearcommunication time. At time t2, the communication controller section1234 transmits the reference signal R. The characteristics informationdeterminer section 1331 and reception information transmitter section1332 of the control circuit 1330 in the in-vehicle terminal 1300 areused to determine, for example, the front antenna propagation pathcharacteristics information CCA and the rear antenna propagation pathcharacteristics information CCB and transmit the determined informationfrom the transmitter 1311 to the base station 1200.

Referring to FIG. 14 (B), the front antenna propagation pathcharacteristics information CCA (t1) indicated by a dotted line is thefront antenna propagation path characteristics information CCA at timet1. Further, the front antenna propagation path characteristicsinformation CCA (t2) indicated by a solid line is the front antennapropagation path characteristics information CCA at time t2.Furthermore, the rear antenna propagation path characteristicsinformation CCB (t2) indicated by another solid line is the rear antennapropagation path characteristics information CCB at time t2.

The rear antenna propagation path characteristics information CCB (t2)in FIG. 14 (B) is the propagation path characteristics information CCthat is determined by allowing the rear antenna 1372 to receive thereference signal R at a position where the reference signal R isreceived by the front antenna 1371. Therefore, the rear antennapropagation path characteristics information CCB (t2) is similar to thefront antenna propagation path characteristics information CCA (t1).This signifies that communication is established at a goodsignal-to-noise ratio when the base station 1200 communicates at time t2with the in-vehicle terminal 1300 by using the resource selected by theresource selector section 1232.

Further, the resource selector section 1232 determines the resource tobe used during the aforementioned rear time post-period. As mentioned,the rear time post-period is a period subsequent to the rearcommunication time and is a predicted period of time required for therear antenna 1372 to reach the position of the front antenna 1371 at therear communication time. FIG. 13 (C) illustrates the position of thein-vehicle terminal 1300 during the rear time post-period.

The position of the rear antenna 1372 in FIG. 13 (C) is intermediatebetween the position of the front antenna 1371 at time t1 in FIG. 13 (A)and the position of the front antenna 1371 at time t2 in FIG. 13 (B).Therefore, as indicated in FIG. 14 (C), an estimated value of the rearantenna propagation path characteristics information CCB (t3) at time t3would be intermediate between the front antenna propagation pathcharacteristics information CCA (t1) at time t1 and the front antennapropagation path characteristics information CCA (t2) at time t2. Therear antenna propagation path characteristics information CCB (t3) inFIG. 13 (C) can be obtained by determining the weighted average of thefront antenna propagation path characteristics information CCA (t1) andthe front antenna propagation path characteristics information CCA (t2)based on the ratio between the distance from the position of the frontantenna 1371 at time t1 to the position of the rear antenna 1372 at timet3 and the distance from the position of the rear antenna 1372 at timet3 to the position of the front antenna 1371 at time t2. Alternatively,depending on the required accuracy, the simple average of the frontantenna propagation path characteristics information CCA (t1) and thefront antenna propagation path characteristics information CCA (t2) maybe determined, instead of the weighted average, to obtain the rearantenna propagation path characteristics information CCB (t3).

Based on the above-described rear antenna propagation pathcharacteristics information CCB about the rear time post-period, theresource selector section 1232 determines the resource for use duringthe rear time post-period. In FIG. 14 (C), the estimated value of therear antenna propagation path characteristics information CCB (t3)indicates that frequencies f9-f10, f11-f12, and f13-f14 form frequencybands having a good signal-to-noise ratio. Therefore, the resourceselector section 1232 selects a frequency channel using such frequencybands as the resource for use at time t3.

The communication controller section 1234 then uses the selectedresource at time t3 to communicate with the in-vehicle terminal 1300 bytransmitting a signal including the ID of the in-vehicle terminal 1300.This establishes communication at a good signal-to-noise ratio even attime t3.

Fifth Embodiment

The mobile communication system according to a fifth embodiment has thesame hardware configuration as the mobile communication system accordingto the fourth embodiment. The control circuit 1330 of the in-vehicleterminal 1300 in the fifth embodiment includes the characteristicsinformation determiner section 1331 and the reception informationtransmitter section 1332, as is the case with the control circuit in thefourth embodiment.

In the fifth embodiment, the reception information transmitter section1332 transmits to the base station 1200 not only various informationtransmitted in the fourth embodiment, but also the current position atwhich the reference signal R is received. In the fifth embodiment,therefore, the reception information transmitter section 1332 furthertransmits, from the transmitter 1311 to the base station 1200, the frontantenna propagation path characteristics information CCA and the rearantenna propagation path characteristics information CCB, which arerespectively determined from the reference signal R received at thefront communication time and the reference signal R received at the rearcommunication time, in addition to the movement speed of the in-vehicleterminal 1300 at the time of reception of the reference signal R, thedistance between the front antenna 1371 and the rear antenna 1372, andthe ID of the in-vehicle terminal 1300.

As in FIG. 15, the storage unit 1220 of the base station 1200 includes areproducibility index database 1224. Further, the control circuit 1230additionally includes a reproducibility determiner section 1235 as inFIG. 15. Elements not depicted in FIG. 15 are identical with theelements in the base station 1200 according to the fourth embodiment.Namely, the elements identical with the elements in the base station1200 according to the fourth embodiment are omitted from FIG. 15.

The reproducibility index database 1224 associates a point (i.e., spot)with the reproducibility index determined by the later-describedreproducibility determiner section 1235.

The reproducibility determiner section 1235 compares the front antennapropagation path characteristics information CCA with the rear antennapropagation path characteristics information CCB, which is determinedfrom the reference signal R transmitted from the base station 1200 atthe rear communication time, and determines the reproducibility indexindicative of reproducibility of the propagation path characteristicsinformation CC. The reproducibility index may be calculated as follows.The reproducibility index is calculated by determining at each frequencythe absolute value of the difference between the signal-to-noise ratioindicated by the front antenna propagation path characteristicsinformation CCA and the signal-to-noise ratio indicated by the rearantenna propagation path characteristics information CCB. The greaterthe integrated value of the absolute value of the difference, the lowerthe reproducibility indicated by the reproducibility index. Further, thereproducibility determiner section 1235 associates the calculatedreproducibility index with a communication position and updates thereproducibility index database 1224 based on the reproducibility indexand the communication position.

Further, in the fifth embodiment, the communication controller section1234 determines the position of communication at the rear communicationtime or during the rear time post-period from the current position andmovement speed of the in-vehicle terminal 1300, which are acquired atthe front communication time. Then, based on the determined position ofcommunication and on the reproducibility index database 1224, thecommunication controller section 1234 determines a parameter setting onthe reliability of communication at the rear communication time orduring the rear time post-period and communicates with the in-vehicleterminal 1300.

A parameter of reliability is, for example, a code rate. The lower thecode rate (i.e., the higher the redundancy), the higher the reliabilityof communication. Therefore, when the reproducibility index indicateslow reproducibility, the code rate is lowered. Another parameter ofreliability is a modulation rate. The higher the modulation rate, thelower the reliability of communication. Therefore, when thereproducibility index indicates low reproducibility, the modulation rateis lowered.

The fifth embodiment thus improves the reliability of communication atthe rear communication time or during the rear time post-period.

Sixth Embodiment

As in FIG. 16, a mobile communication system 2000 according to a sixthembodiment includes a first in-vehicle terminal 2200 and a secondin-vehicle terminal 2300. The first in-vehicle terminal 2200 is mountedin a vehicle 6; the second in-vehicle terminal 2300 is mounted in avehicle 4. The mobile communication system 2000 may include a pluralityof first in-vehicle terminals 2200 and a plurality of second in-vehicleterminals 2300. The vehicle 6 corresponds to a first mobile object,while the first in-vehicle terminal 2200 mounted in the vehicle 6corresponds to the target communication apparatus. The vehicle 4corresponds to a second mobile object, while the second in-vehicleterminal 2300 mounted in the vehicle 4 corresponds to the mobilecommunication apparatus.

First, a configuration of the second in-vehicle terminal 2300 will bedescribed. Obviously from FIG. 17, the second in-vehicle terminal 2300has the same hardware configuration as the in-vehicle terminal 1300according to the fourth embodiment.

Thus a communicator 2310 includes a transmitter 2311, a receiver 2312, afront antenna 2371, and a rear antenna 2372. These elements have thesame configurations as the transmitter 1311, receiver 1312, frontantenna 1371, and rear antenna 1372 included in the communicator 1310 inFIG. 10. Like the front antenna 1371 and the rear antenna 1372, thefront antenna 2371 and the rear antenna 2372 are mounted on the roof ofthe vehicle 4 with a front-rear relation (i.e., longitudinally disposedin the travel direction of the vehicle 4), and positioned at the sameheight. In the sixth embodiment, the front antenna 2371 functions as thereference antenna; the rear antenna 2372 functions as the selectedresource antenna.

Further, a storage unit 2320 is identical with the storage unit 1320 inFIG. 10. A control circuit 2330 includes a CPU 2340, a ROM 2350, and aRAM 2360. Signals from the speed sensor 41 and the position detector 42are inputted to the control circuit 2330.

As in FIG. 18, the control circuit 2330 includes functions differentfrom those of the control circuit 1330 in FIG. 10. Specifically, thecontrol circuit 2330 includes, as its functions, an outgoing signalgenerator section 2331 and a communication controller section 2332.

The outgoing signal generator section 2331 periodically generates asecond terminal signal St2, which is transmitted from the transmitter2311. The second terminal signal St2 includes the reference signal R, asignal indicative of the movement speed of the second in-vehicleterminal 2300, and a signal indicative of an inter-antenna distance. Themovement speed of the second in-vehicle terminal 2300 is a speed that isacquired from the speed sensor 41. The inter-antenna distance is thedistance between the front antenna 2371 and the rear antenna 2372. Ifthe first in-vehicle terminal 2200 stores the inter-antenna distancebeforehand, the second terminal signal St2 does not need to include theinter-antenna distance.

The communication controller section 2332 controls the transmitter 2311so as to let the front antenna 2371 transmit the second terminal signalSt2 generated by the outgoing signal generator section 2331. Time t1 inFIG. 16 (A) is the time of such signal transmission. Upon receipt of thesecond terminal signal St2, the first in-vehicle terminal 2200 transmitsa first terminal signal St1 to the second in-vehicle terminal 2300 byusing a resource determined based on the reference signal R included inthe second terminal signal St2. The communication controller section2332 controls the receiver 2312 so as to let the rear antenna 2372receive the first terminal signal St1.

A configuration of the first in-vehicle terminal 2200 will be described.Obviously from FIG. 19, the first in-vehicle terminal 2200 has the samehardware configuration as the second in-vehicle terminal 2300.Specifically, the first in-vehicle terminal 2200 includes a communicator2210, a storage unit 2220, and a control circuit 2230. These elementshave the same configurations as the communicator 2310, storage unit2320, and control circuit 2330 in the second in-vehicle terminal 2300.

The communicator 2210 includes a transmitter 2211, a receiver 2212, atarget apparatus front antenna 2271, and a target apparatus rear antenna2272. These elements have the same configurations as the transmitter2311, receiver 2312, front antenna 2371, and rear antenna 2372 includedin the communicator 2310 of the second in-vehicle terminal 2300. Thetarget apparatus front antenna 2271 and the target apparatus rearantenna 2272 are mounted on the roof of the vehicle 6, longitudinallydisposed in the travel direction of the vehicle 6, and positioned at thesame height. The distance between the target apparatus front antenna2271 and the target apparatus rear antenna 2272 is the same as thedistance between the front antenna 2371 and the rear antenna 2372.

The control circuit 2230 includes a CPU 2240, a ROM 2250, and a RAM2260. Signals from the speed sensor 41 and the position detector 42 areinputted to the control circuit 2230.

The control circuit 2230 has functions in FIG. 20. Specifically, thecontrol circuit 2230 includes, as its functions, a characteristicsinformation determiner section 2231, a propagation path characteristicsacquirer section 2232, a resource selector section 2233, a timingdeterminer section 2234, and a communication controller section 2235.

As mentioned, the second in-vehicle terminal 2300 transmits the secondterminal signal St2. When the second terminal signal St2 is received bythe target apparatus front antenna 2271, the characteristics informationdeterminer section 2231 assumes that the second in-vehicle terminal 2300is in the communication position at the time of reception, that is, atthe time of transmission from the second in-vehicle terminal 2300.

Further, the characteristics information determiner section 2231determines the propagation path characteristics information CC based onthe reference signal R included in the received second terminal signalSt2. The determined propagation path characteristics information CC isthen stored in the storage unit 2220. In the embodiment, the storageunit 2220 stores the propagation path characteristics information CC.Alternatively, a different storage unit may be designated to store thepropagation path characteristics information CC. FIG. 21 illustrates thepropagation path characteristics information CC determined by thecharacteristics information determiner section 2231.

The propagation path characteristics acquirer section 2232 acquires thepropagation path characteristics information CC from the storage unit2220. The resource selector section 2233 selects a resource for use incommunication at the communication position determined by thecharacteristics information determiner section 2231 based on thepropagation path characteristics information CC acquired by thepropagation path characteristics acquirer section 2232. The meaning ofthe resource and the method of resource selection are the same asdescribed in conjunction with the resource selector section 235 in thefirst embodiment. When a frequency resource to be used for communicationis to be selected based on the propagation path characteristicsinformation CC illustrated in FIG. 21, frequencies f15-f16, f17-f18, andf19-f20 form frequency bands having a good signal-to-noise ratio asindicated in FIG. 21. Therefore, the resource selector section 2233selects a frequency channel using such frequency bands as the resourcefor use at the communication position.

The timing determiner section 2234 predicts the time at which the rearantenna 2372 attached to the second in-vehicle terminal 2300 is placedat a position where the second terminal signal St2 is transmitted fromthe front antenna 2371, that is, at the communication positiondetermined by the characteristics information determiner section 2231.The time to be predicted can be calculated by adding a value obtained bydividing the inter-antenna distance between the rear antenna 2372 andthe front antenna 2371 by the movement speed to the time of reception ofthe second terminal signal St2.

At the time determined by the timing determiner section 2234, thecommunication controller section 2235 transmits the first terminalsignal St1 to the second in-vehicle terminal 2300 by using the resourceselected by the resource selector section 2233 from either the targetapparatus front antenna 2271 or the target apparatus rear antenna 2272,whichever is closer to the position of the target apparatus frontantenna 2271 at the time of reception of the second terminal signal St2.The contents of the first terminal signal St1 are not particularlylimited. As mentioned, the second in-vehicle terminal 2300 uses the rearantenna 2372 to receive the first terminal signal St1.

The communication controller section 2235 transmits a signal at theabove-mentioned time on transmission condition that the secondin-vehicle terminal 2300 and the first in-vehicle terminal 2200 be equalin movement speed. The reason is that the communication environment forthe second terminal signal St2 is not similar to the communicationenvironment for the first terminal signal St1 if the second in-vehicleterminal 2300 and the first in-vehicle terminal 2200 are not equal inmovement speed. Further, conditions of being equal in travel directionand of traveling on the same road may be imposed in addition to thecondition of being equal in movement speed.

The movement speed of the second in-vehicle terminal 2300 is included inthe second terminal signal St2, and the movement speed of the firstin-vehicle terminal 2200 is determined from a signal of the speed sensor41 mounted in the vehicle 6. Obviously, the condition of being equal inmovement speed includes the condition of being substantially equal inmovement speed. The degree of tolerable difference in the movement speedis set as appropriate.

If the above transmission condition is not established and the movementspeed of the second in-vehicle terminal 2300 or first in-vehicleterminal 2200 is zero or low and close to zero, a terminal exhibiting amovement speed of zero or close to zero can be handled in the samemanner as the base station 1200. Therefore, if the transmissioncondition is not established and the movement speed of the secondin-vehicle terminal 2300 or first in-vehicle terminal 2200 is zero orlow and close to zero, the timing determiner section 2234 and thecommunication controller section 2235 provide the same control as thetiming determiner section 1233 and communication controller section 1234according to the fourth embodiment.

Time t2 in FIG. 16 (B) is the time determined by the timing determinersection 2234. In FIG. 16 (B), a signal is transmitted from the targetapparatus rear antenna 2272. Obviously from the comparison between FIG.16 (A) and FIG. 16 (B), the position of the front antenna 2371 when thesecond terminal signal St2 is communicated is the same as the positionof the rear antenna 2372 when the first terminal signal St1 iscommunicated. Further, the position of the target apparatus frontantenna 2271 when the second terminal signal St2 is communicated is thesame as the position of the target apparatus rear antenna 2272 when thefirst terminal signal St1 is communicated. Therefore, the communicationenvironment for the second terminal signal St2 is very similar to thecommunication environment for the first terminal signal St1.Consequently, the first terminal signal St1 can be properly communicatedby using a resource that is selected based on the propagation pathcharacteristics information CC determined from the reference signal Rincluded in the second terminal signal St2.

FIG. 16 (B) depicts an easy-to-understand example in which the positionsof two antennas 2271, 2371 for the communication of the second terminalsignal St2 are the same as the positions of two antennas 2272, 2372 forthe communication of the first terminal signal St1.

However, signals are generally transmitted at discrete time intervals.Therefore, the communication controller section 2235 may fail totransmit the first terminal signal St1 at an exact time determined bythe timing determiner section 2234. The “time determined by the timingdeterminer section 2234”, which is mentioned earlier to describe thecommunication controller section 2235, denotes a time that permits asignal transmission and is closest to the time determined by the timingdeterminer section 2234.

The time determined by the timing determiner section 2234 does notalways coincide with a time that permits a signal transmission.Therefore, at the time that permits a signal transmission, the targetapparatus front antenna 2271 may be closer to the position of the targetapparatus front antenna 2271 at the time of reception of the secondterminal signal St2 than the target apparatus rear antenna 2272. Thus,the communication controller section 2235 transmits the first terminalsignal St1 from either the target apparatus front antenna 2271 or thetarget apparatus rear antenna 2272, whichever is closer to the positionof the target apparatus front antenna 2271 at the time of reception ofthe second terminal signal St2.

For convenience of explanation, the sixth embodiment has been describedon the assumption that the control circuit 2230 of the first in-vehicleterminal 2200 differs in functionality from the control circuit 2330 ofthe second in-vehicle terminal 2300. Alternatively, both of the controlcircuits 2230, 2330 may incorporate all the functions in FIGS. 18 and20. In such an alternative configuration, the functions of the controlcircuit 2330 in the second in-vehicle terminal 2300 should be executedif the second terminal signal St2 is not received, and the functions ofthe control circuit 2230 in the first in-vehicle terminal 2200 should beexecuted if the second terminal signal St2 is received.

Seventh Embodiment

As in FIG. 22, a mobile communication system 3000 according to a seventhembodiment includes a first in-vehicle terminal 3200 and a secondin-vehicle terminal 3300. The first in-vehicle terminal 3200 is mountedin the vehicle 4, and the second in-vehicle terminal 3300 is mounted inthe vehicle 6. The mobile communication system 3000 may include aplurality of first in-vehicle terminals 3200 and a plurality of secondin-vehicle terminals 3300.

The first in-vehicle terminal 3200 includes a first antenna 3271, asecond antenna 3272, and a third antenna 3273. These antennas 3271,3272, 3273 are equal in structure, longitudinally disposed in the traveldirection of the vehicle 6, positioned at the same height, and arrangedat equal intervals.

The second in-vehicle terminal also includes three antennas, namely, afirst antenna 3371, a second antenna 3372, and a third antenna 3373.These antennas 3371, 3372, 3373 are equal in structure to the antennas3271, 3272, 3273, longitudinally disposed in the travel direction of thevehicle 4, positioned at the same height, and arranged at equalintervals. Further, the antennas 3371, 3372, 3373 are arranged at thesame intervals as the antennas 3271, 3272, 3273.

As in FIG. 23, the first in-vehicle terminal 3200 has the same hardwareconfiguration as the first in-vehicle terminal 2200 according to thesixth embodiment except that the former includes three antennas, namely,the first antenna 3271, the second antenna 3272, and the third antenna3273.

As in FIG. 24, the second in-vehicle terminal 3300 has the same hardwareconfiguration as the second in-vehicle terminal 2300 according to thesixth embodiment except that the former includes three antennas, namely,the first antenna 3371, the second antenna 3372, and the third antenna3373.

A control circuit 3230 of the first in-vehicle terminal 3200 has thesame functions as a control circuit 3330 of the second in-vehicleterminal 3300. As in FIG. 25, the control circuit 3230 of the firstin-vehicle terminal 3200 includes a characteristics informationdeterminer section 3231, a propagation path characteristics acquirersection 3232, a timing determiner section 3233, a resource selectorsection 3234, an outgoing signal generator section 3235, and acommunication controller section 3236.

As in FIG. 26, the control circuit 3330 of the second in-vehicleterminal 3300 includes a characteristics information determiner section3331, a propagation path characteristics acquirer section 3332, a timingdeterminer section 3333, a resource selector section 3334, an outgoingsignal generator section 3335, and a communication controller section3336.

The seventh embodiment alternately gives rise to a state where the firstin-vehicle terminal 3200 functions as the target communication apparatusand the second in-vehicle terminal 3300 functions as the mobilecommunication apparatus and a state where the first in-vehicle terminal3200 functions as the mobile communication apparatus and the secondin-vehicle terminal 3300 functions as the target communicationapparatus. In the former state, the vehicle 6 corresponds to the firstmobile object, and the vehicle 4 corresponds to the second mobileobject. In the latter state, the vehicle 6 corresponds to the secondmobile object, and the vehicle 4 corresponds to the first mobile object.

As mentioned, the control circuit 3230 of the first in-vehicle terminal3200 has the same functions as the control circuit 3330 of the secondin-vehicle terminal 3300. The functions of only the control circuit 3230of the first in-vehicle terminal 3200 will be described in detail.

First of all, the outgoing signal generator section 3235 will bedescribed. The outgoing signal generator section 3235 generates anestimation signal Sc, which is to be transmitted from a transmitter3311. The estimation signal Sc is similar to the second terminal signalSt2 in the sixth embodiment, and includes the reference signal R, asignal indicative of the movement speed of an in-vehicle terminaltransmitting the estimation signal Sc (the first in-vehicle terminal3200 in the embodiment), and a signal indicative of the inter-antennadistance. The inter-antenna distance is the distance between the secondantenna 3272 and the third antenna 3273. If the second in-vehicleterminal 3300 stores the inter-antenna distance beforehand, theestimation signal Sc does not need to include the inter-antennadistance. The estimation signal Sc may be transmitted together withvarious known signals (hereinafter referred to as the main signals)transmitted and received during vehicle-to-vehicle communication. Themain signals include signals notifying surrounding vehicles of thebehavior of the vehicle 4, such as signals indicative of theacceleration and the current position.

The communication controller section 3236 controls a transmitter 3211 soas to transmit the estimation signal Sc, which is generated by theoutgoing signal generator section 3235, from the second antenna 3272. Inthis instance, the second antenna 3272 functions as the front antennaand as the reference antenna. Meanwhile, when the second antenna 3372 ofthe second in-vehicle terminal 3300 transmits the estimation signal Sc,the second antenna 3372 functions as the front antenna and as thereference antenna.

FIG. 22 (A) illustrates a state where the outgoing signal generatorsection 3335 and communication controller section 3336 of the secondin-vehicle terminal 3300 perform, at time ti, the same process as theoutgoing signal generator section 3235 and the communication controllersection 3236 to transmit the estimation signal Sc from the secondantenna 3372. The first in-vehicle terminal 3200 receives the estimationsignal Sc through the first antenna 3271, the second antenna 3272, andthe third antenna 3273. Parenthesized symbols in FIG. 22 correlates tosymbols used in FIG. 27 with respect to the antennas.

When the estimation signal Sc is received by the first antenna 3271, thesecond antenna 3272, and the third antenna 3273, the characteristicsinformation determiner section 3231 assumes that the second in-vehicleterminal 3300 is at the communication position at the time of reception,that is, at the time of transmission from the second in-vehicle terminal3300.

Further, the characteristics information determiner section 3231determines the propagation path characteristics information CC based onthe reference signal R included in the estimation signal Sc. Thedetermined propagation path characteristics information CC is thenstored in a storage unit 3220.

FIG. 27 (A) illustrates the propagation path characteristics informationCC determined by the characteristics information determiner section 3231based on the estimation signal Sc received at time t1. FIG. 27 (A)depicts three propagation path characteristics informations CC. Thepropagation path characteristics information CCA1-B2 (t1) is propagationpath characteristics information CC that is determined by receiving,with the first antenna 3271, the estimation signal Sc transmitted fromthe second antenna 3372. The propagation path characteristicsinformation CCB1-B2 (t1) is propagation path characteristics informationCC that is determined by receiving, with the second antenna 3272, theestimation signal Sc transmitted from the second antenna 3372. Thepropagation path characteristics information CCC1-B2 (t1) is propagationpath characteristics information CC that is determined by receiving,with the third antenna 3273, the estimation signal Sc transmitted fromthe second antenna 3372.

The propagation path characteristics acquirer section 3232 acquires,from the storage unit 3220, three propagation path characteristicsinformations CC that are determined by using signals received throughthe first antenna 3271, the second antenna 3272, and the third antenna3273.

The timing determiner section 3233 predicts (i.e., determines inadvance) the time at which the third antenna 3373 of the secondin-vehicle terminal 3300 is placed at a position at which the estimationsignal Sc is received by the second antenna 3372, that is, thecommunication position determined by the characteristics informationdeterminer section 3231. The above time can be calculated by adding avalue obtained by dividing the inter-antenna distance between the secondantenna 3372 and the third antenna 3373 by the movement speed to thetime of reception of the estimation signal Sc.

Based on the three propagation path characteristics informations CCacquired by the propagation path characteristics acquirer section 3232,the resource selector section 3234 selects a resource for communicationat the communication position determined by the characteristicsinformation determiner section 3231. The meaning of the resource and themethod of resource selection are the same as described in conjunctionwith the resource selector section 235 in the first embodiment. Whenselecting a resource, the resource selector section 3234 uses themovement speed included in the estimation signal Sc, the movement speedof the first in-vehicle terminal 3200, and the time determined by thetiming determiner section 3333. The difference in speed between thefirst in-vehicle terminal 3200 and the second in-vehicle terminal 3300can be calculated from the difference between the two movement speeds.The calculated speed difference is then multiplied by the interval oftime between the current time and the time determined by the timingdeterminer section 3333. This can calculate the amount of change in thedistance (hereinafter referred to as the change distance) between thefirst in-vehicle terminal 3200 and the second in-vehicle terminal 3300at the time determined by the timing determiner section 3233 relative tothe distance between the first in-vehicle terminal 3200 and the secondin-vehicle terminal 3300 at the time of communication of the estimationsignal Sc.

Consequently, it can be estimated that, at the time determined by thetiming determiner section 3233, the second antenna 3272 will be placedat a position shifted toward the first antenna 3271 or the third antenna3273 by the change distance as compared to the position of reception ofthe estimation signal Sc.

The resource selector section 3234 uses the above estimation todetermine an estimated value of the propagation path characteristicsinformation CC that prevails when the second antenna 3272 is used at thetime determined by the timing determiner section 3233. Two propagationpath characteristics informations CC are used to determine the estimatedvalue of propagation path characteristics information. The firstinformation is the propagation path characteristics information CCB1-B2(t1) associated with the second antenna 3272. The second information iseither the propagation path characteristics information CCA1-B2 (t1) orthe propagation path characteristics information CCC1-B2 (t1), whicheveris associated with an antenna positioned close to the second antenna3272 at the time determined by the timing determiner section 3233. Thesetwo propagation path characteristics informations CC are, for example,extrapolated or interpolated at the ratio of the change distance to theinter-antenna distance to determine the estimated value of thepropagation path characteristics information CC that prevails when thesecond antenna 3272 is used at the time determined by the timingdeterminer section 3233.

The propagation path characteristics information CC represented by asolid line in FIG. 27 (B) is an estimated value of propagation pathcharacteristics information CCB1-B2 (t2) at time t2, which is the timedetermined by the timing determiner section 3233. Dotted lines in FIG.27 (B) represent the three propagation path characteristics informationsCC in FIG. 27 (A), which are depicted for comparison purposes. Theestimated value of the propagation path characteristics informationCCB1-B2 (t2) in FIG. 27 (B) indicates that the first in-vehicle terminal3200 is higher in movement speed than the second in-vehicle terminal3300. At the time determined by the timing determiner section 3233,therefore, the second antenna 3272 is positioned more forward in thetravel direction of the vehicle 6 than the position of the first antenna3271 at the time of reception of estimation signal Sc, as indicated inFIG. 22 (B). Consequently, the estimated value of the propagation pathcharacteristics information CCB1-B2 (t2) is determined by extrapolationfrom the propagation path characteristics information CCB1-B2 (t1) andthe propagation path characteristics information CCA1-B2 (t1).

The determined estimated value of the propagation path characteristicsinformation CCB1-B2 (t2) is then used to select a resource forcommunication at the communication position, as is the case with thesixth embodiment.

The outgoing signal generator section 3235 not only generates theestimation signal Sc as described, but also generates the estimationsignal Sc even when the communication position is determined and aresource for use at the communication position is selected. Further, theoutgoing signal generator section 3235 also generates the main signals.

At the time determined by the timing determiner section 3233, thecommunication controller section 3236 transmits from the second antenna3272 the estimation signal Sc and main signals generated by the outgoingsignal generator section 3235. In this instance, the second antenna 3272functions as the target apparatus rear antenna. The first antenna 3271positioned forward of the second antenna 3272 corresponds to the targetapparatus front antenna.

The above state prevails at time t2 in FIG. 22 (B). The reference signalR, which is among the estimation signal Sc and main signals, isallocated to all subchannels. The other signals are transmitted by usinga resource selected by the resource selector section 3234.

In FIG. 22 (B), the second in-vehicle terminal 3300 receives theestimation signal Sc through the first antenna 3371, the second antenna3372, and the third antenna 3373. In this instance, the third antenna3373 is at the communication position and functions as the rear antennaand as the selected resource antenna. The signal received through thethird antenna 3373 provides highly reliable communication.

The characteristics information determiner section 3331, which has thesame function as the characteristics information determiner section3231, determines the propagation path characteristics information CCfrom the estimation signal Sc received through the first antenna 3371,the second antenna 3372, and the third antenna 3373. The position of thesecond antenna 3372 at the time of reception is regarded as thecommunication position. FIG. 27 (C) illustrates three propagation pathcharacteristics informations CCA2-B1 (t2), CCB2-B1 (t2), CCC2-B1 (t2),which are determined by the characteristics information determinersection 3331 from the estimation signal Sc received at time t2.

The propagation path characteristics acquirer section 3332 acquires thethree propagation path characteristics informations CCA2-B1 (t2),CCB2-B1 (t2), CCC2-B1 (t2) from a storage unit 3320. The timingdeterminer section 3333 predicts the time at which the third antenna3273 of the first in-vehicle terminal 3200 is placed at a position wherethe estimation signal Sc is received by the second antenna 3272, thatis, at the communication position determined by the characteristicsinformation determiner section 3331. The predicted time is regarded astime t3.

Based on the three propagation path characteristics informations CCdetermined by propagation path characteristics acquirer section 3332,the resource selector section 3334 selects a resource for communicationat the communication position determined by the characteristicsinformation determiner section 3331. For resource selection, theresource selector section 3334 performs the same process as the resourceselector section 3234 to determine the estimated value of propagationpath characteristics information CCB2-C1 (t3) in FIG. 27 (D). In FIG. 27(D), too, the three propagation path characteristics informations CC inFIG. 27 (C) are represented by dotted lines for comparison purposes. Theresource for use at the communication position is selected based on theestimated value of the propagation path characteristics informationCCB2-C1 (t3).

The outgoing signal generator section 3335 generates the estimationsignal Sc and the main signals. Then, at time t3, the communicationcontroller section 3336 transmits the estimation signal Sc and the mainsignals from the second antenna 3372. This state is illustrated in FIG.22 (C). A comparison between FIG. 22 (A) and FIG. 22 (C) indicates thatthe states illustrated in FIG. 22 (A) and FIG. 22 (C) are the sameexcept for the positions of the vehicles 4, 6. Consequently, the seventhembodiment ensures that highly reliable bidirectional communication canbe repeatedly established between the first in-vehicle terminal 3200 andthe second in-vehicle terminal 3300.

Eighth Embodiment

As in FIG. 28, a mobile communication system 4000 according to an eighthembodiment includes a base station 4200 and an in-vehicle terminal 4300.The base station 4200 corresponds to the target communication apparatus.The in-vehicle terminal 4300 corresponds to the mobile communicationapparatus. The mobile communication system 4000 may include a pluralityof base stations 4200 and a plurality of in-vehicle terminals 4300.

[Configuration of in-Vehicle Terminal 4300]

As in FIG. 28, the in-vehicle terminal 4300 includes a plurality ofantenna elements 4313. The antenna elements 4313 are equal in structure,mounted on the roof of the vehicle 4, positioned at the same height, andperiodically disposed.

A MIMO technology is applied to the antenna elements 4313 so that theantenna elements 4313 are dynamically allocated to two antennas, namely,a front antenna 4313A and a rear antenna 4313B. Specifically, the frontantenna 4313A and the rear antenna 4313B are antenna element groups thatinclude a plurality of antenna elements 4313. The front antenna 4313Afunctions as the reference antenna, and the rear antenna 4313B functionsas the selected resource antenna.

As in FIG. 29, the in-vehicle terminal 4300 includes a communicator4310, a storage unit 4320, and a control circuit 4330. The communicator4310 includes a transmitter 4311 and a receiver 4312 in addition to theantenna elements 4313. The transmitter 4311 and the receiver 4312 usethe antenna elements 4313 for transmission and reception purposes. Thetransmitter 4311 and the receiver 4312 have the same functions as thetransmitter 1311 and receiver 1312 according to the fourth embodimentexcept that the former transmitter and receiver use the antennaelements.

As in FIG. 30, the control circuit 4330 includes, as its functions, acharacteristics information determiner section 4331, a communicationcontroller section 4332, and a reception status signal transmittersection 4333.

First of all, the characteristics information determiner section 4331will be described. In the eighth embodiment, too, the base station 4200periodically transmits the reference signal R. The in-vehicle terminal4300 receives the reference signal R through the front antenna 4313A andthe rear antenna 4313B. The antenna elements 4313 forming the frontantenna 4313A and the rear antenna 4313B may be determined in advance bythe control circuit 4330 of the in-vehicle terminal 4300. Alternatively,the base station 4200 may make such a determination and notify thein-vehicle terminal 4300 of the determined antenna elements 4313simultaneously with or prior to the reference signal R.

The characteristics information determiner section 4331 acquires thereference signal R received by the antenna elements 4313 from thereceiver 4312. The characteristics information determiner section 4331then determines the propagation path characteristics information CC withrespect to all antenna elements 4313 that are included in the frontantenna 4313A and the rear antenna 4313B and used for transmission fromthe base station 4200. The propagation path characteristics informationCC may be determined in the same manner as described in conjunction withthe foregoing embodiments.

The communication controller section 4332 determines antenna elements4313 for use as the front antenna 4313A and the rear antenna 4313B fromthe antenna elements 4313, and configures the front antenna 4313A andthe rear antenna 4313B accordingly. The front antenna 4313A and the rearantenna 4313B receive the reference signal R. The rear antenna 4313Breceives the reference signal R to determine the reproducibility index.If the reproducibility index is not to be determined, the rear antenna4313B does not need to receive the reference signal R.

To determine the antenna elements 4313 to be allocated to the frontantenna 4313A and the rear antenna 4313B, the communication controllersection 4332 uses the movement speed of the in-vehicle terminal 4300 anda transmission cycle in which the base station 4200 transmits a signal.The distance moved by the in-vehicle terminal 4300 during onetransmission cycle is calculated by multiplying the movement speed ofthe in-vehicle terminal 4300 by the transmission cycle in which the basestation 4200 transmits a signal.

The allocation of the antenna elements 4313 is determined in such amanner that the distance between associated antenna elements 4313 of thefront antenna 4313A and rear antenna 4313B (hereinafter referred to asthe inter-antenna distance) d is equal to or longer than the distancemoved by the in-vehicle terminal 4300 during one transmission cycle.

Further, the antenna elements 4313 to be allocated to the front antenna4313A and the rear antenna 4313B are selected in such a manner that theantenna elements 4313 forming the front antenna 4313A and the antennaelements 4313 forming the rear antenna 4313B are arranged in the samepattern.

The allocation may be determined in advance by the base station 4200 andreported to the in-vehicle terminal 4300. When the in-vehicle terminal4300 determines the allocation, the transmission cycle in which the basestation 4200 transmits a signal can be acquired by the in-vehicleterminal 4300 as far as a signal indicative of the transmission cycle istransmitted from the base station 4200 and received by the in-vehicleterminal 4300. An alternative is to receive and measure a signaltransmitted from the base station 4200. FIG. 31 illustrates anallocation example in which the front antenna 4313A and the rear antenna4313B are allocated. FIG. 32 illustrates another allocation example inwhich the front antenna 4313A and the rear antenna 4313B are allocated.In FIGS. 31 and 32, the antenna elements 4313 forming the front antenna4313A and the antenna elements 4313 forming the rear antenna 4313B arearranged in the same pattern.

Further, the inter-antenna distance d is d1 in FIG. 31 and d2 in FIG.32. The distance d2 is shorter than the distance d1. As described, theinter-antenna distance d can be changed by changing the allocation ofthe antenna elements 4313.

The reception status signal transmitter section 4333 transmits areception status signal Sr from the transmitter 4311 to the base station4200. The reception status signal Sr includes (i) the movement speed andcurrent position of the in-vehicle terminal 4300 at the time ofreception of the reference signal R, (ii) the inter-antenna distance d,(iii) the ID of the in-vehicle terminal 4300, and (iv) the followingpropagation path characteristics information CC. That is, thepropagation path characteristics information CC is about allcombinations between (i) antenna elements 4313 forming the front antenna4313A and antenna elements 4313 forming the rear antennas 4313B and (ii)the antenna elements 4213 used for transmission from the base station4200.

FIG. 28 (A) illustrates a state where the reference signal R istransmitted from the base station 4200 at time t1 and the receptionstatus signal Sr is subsequently transmitted from the in-vehicleterminal 4300.

[Configuration of Base Station 4200]

As in FIG. 33, the base station includes a plurality of antenna elements4213 in place of the antenna 213 in FIG. 2. The other hardwareconfiguration is the same as that of the base station 200 according tothe first embodiment. Specifically, the base station 4200 includes acommunicator 4210, a storage unit 4220, and a control circuit 4230. Thecommunicator 4210 includes a transmitter 4211 and a receiver 4212. Thecontrol circuit 4230 includes a CPU 4240, a ROM 4250, and a RAM 4260.

The storage unit 4220 stores a reproducibility index database 4221 and aroad map database 4222. In the reproducibility index database 4221, areproducibility index determined by a later-described reproducibilitydeterminer section 4235 is associated with a point (i.e., spot).

As in FIG. 34, the control circuit 4230 includes, as its functions, apropagation path characteristics acquirer section 4231, a resourceselector section 4232, a timing determiner section 4233, a communicationcontroller section 4234, and the reproducibility determiner section4235.

The propagation path characteristics acquirer section 4231 acquires fromthe receiver 4212 the propagation path characteristics information CCthat is transmitted from the in-vehicle terminal 4300 and received bythe receiver 4212. The acquired propagation path characteristicsinformation CC associated with the front antenna 4313A is regarded asthe front antenna propagation path characteristics information CCA, andthe acquired propagation path characteristics information CC associatedwith the rear antenna 4313B is regarded as the rear antenna propagationpath characteristics information CCB. It is assumed that the propagationpath characteristics information CC is acquired when the in-vehicleterminal 4300 is at the reception position (i.e., at the communicationposition). Namely, the front antenna propagation path characteristicsinformation CCA and the rear antenna propagation path characteristicsinformation CCB are associated with the communication position.

The resource selector section 4232 regards the position where thereference signal R is received by the front antenna 4371A as thecommunication position, and determines the resource to be used forcommunication at the communication position based on the front antennapropagation path characteristics information CCA acquired by thepropagation path characteristics acquirer section 4231. The resourceselector section 4232 acquires a reproducibility index associated withthe reception position from the reproducibility index database 4221 andselects a resource by using the reproducibility index in addition to thefront antenna propagation path characteristics information CCA.

FIG. 35 illustrates the relationship between an index used by theresource selector section 4232 to select a resource and a pattern of useof the antenna elements 4313. The reproducibility index is acquired fromthe reproducibility index database 4221 and associated with thereception position.

The amount of resource having an estimated signal-to-noise ratio equalto or higher than a standard is determined from propagation pathcharacteristics information CC estimated at the communication position.The propagation path characteristics information CC estimated at thecommunication position is determined in the same manner as described inconjunction with the fifth embodiment.

The amount of resource having an estimated signal-to-noise ratio equalto or higher than the standard may be determined from the determinedpropagation path characteristics information CC by using the same methodas exercised in conjunction with the well-known MIMO technology. Forexample, the signal-to-noise ratio of each resource that prevails whenbeamforming, diversity coding, spatial multiplexing (multistreaming), ora combination of these is performed by using a well-known technology isestimated based on propagation path characteristics information, andthen the amount of resource having a signal-to-noise ratio equal to orhigher than the standard is determined. However, for the sake ofsimplicity, FIG. 35 merely illustrates some patterns that usebeamforming, diversity coding, or spatial multiplexing. The “resource”of the “amount of resource” has the same meaning as in the foregoingembodiments. However, the embodiment uses the MIMO technology.Therefore, resources selected by the resource selector section 4232include a spatial resource that permits the MIMO technology to generatethe degree of freedom of determination. The spatial resource isdetermined by selecting an antenna element use pattern.

A maximum speed is determined by further considering the modulation rateavailable for each resource, that is, the amount of data transmittableper resource. The available modulation rate is determined based on theestimated signal-to-noise ratio. The method of determining the availablemodulation rate may be the same as exercised in conjunction with awell-known adaptive modulation technology. For the sake of simplicity,FIG. 35 indicates values that can be obtained when the ratio of theresource amount to the maximum speed is 3:1. These values are applicableto a case where all resources having an estimated signal-to-noise ratioequal to or higher than the standard are used at the same modulationrate.

The resource selector section 4232 selects a resource for the nextcommunication from indexes illustrated in FIG. 35 and indexes importantfor the next communication. When the reliability of communication is animportant index, directivity 2 of singlestreaming, which is a usepattern exhibiting high reproducibility and involving a large amount ofresource having an estimated signal-to-noise ratio equal to or higherthan the standard, is selected as an antenna use pattern that determinesthe spatial resource. Meanwhile, when the communication speed is animportant index, multistreaming with two streams exhibiting the highestmaximum speed is selected as the antenna use pattern. The method ofselecting a frequency and a time resource is the same as described inconjunction with the foregoing embodiments.

Based on the movement speed of the in-vehicle terminal 4300, which isreceived by the receiver 4212, the timing determiner section 4233determines the rear communication time, which is the time at which therear antenna 4313B is placed at a position where the reference signal Ris received by the front antenna 4313A.

The communication controller section 4234 periodically transmits thereference signal R from the transmitter 4211. Further, at the rearcommunication time determined by the timing determiner section 4233, thecommunication controller section 4234 transmits a predetermined signalto the in-vehicle terminal 4300 by using a resource that is selected bythe resource selector section 4232 as the resource for use at the rearcommunication time. Furthermore, in addition to the predeterminedsignal, the reference signal R is transmitted by using all thesubchannels, as is the case with the fifth embodiment. The communicationcontroller section 4234 corresponds to the target apparatuscommunication controller section.

The reproducibility determiner section 4235 determines thereproducibility index indicative of reproducibility of the propagationpath characteristics information CC by comparing the front antennapropagation path characteristics information CCA with the rear antennapropagation path characteristics information CCB, which is determinedfrom the reference signal R transmitted from the base station 4200 atthe rear communication time. The reproducibility determiner section 4235may determine the reproducibility index in the same manner as thereproducibility determiner section 1235 according to the fifthembodiment. Further, the reproducibility determiner section 4235associates the determined reproducibility index with the communicationposition, and updates the reproducibility index database 4221 based onthe determined reproducibility index and the communication position. Theupdated reproducibility index database 4221 is used at the time ofresource selection as described.

While the embodiments of the present disclosure have been describedabove, it should be understood that the present disclosure is notlimited to the above-described embodiments. The following modificationsare also included in the technical scope of the present disclosure.Further, in addition to the following modifications, various othermodifications may be made without departing from the spirit of thepresent disclosure.

<First Modification>

FIG. 3 depicts the propagation path characteristics information CC byillustrating the relationship between signal-to-noise ratio andfrequency. However, an alternative is to use the relationship betweensignal-to-noise ratio and impulse response instead of frequency.

<Second Modification>

The eighth embodiment may differently be configured to determine areproducibility index by comparing signals successively transmitted fromthe in-vehicle terminal 4300 while eliminating the reproducibility indexdatabase 4221. Such configuration does not allow the reproducibilityindex to represent the reproducibility at exactly the same position.However, the eighth embodiment, which only adopts the reproducibilityindex for determining the use pattern, can still utilize the abovereproducibility index even failing to represent the reproducibility atexactly the same position. Further, the reproducibility index is notessential to determine the use pattern.

<Third Modification>

The foregoing embodiments assume the mobile object as an automobile.Alternatively, the mobile object may be a railroad vehicle, a bicycle,or a pedestrian. When the mobile communication apparatus is held by apedestrian, the radio wave propagation map 221 may be created for eachof a plurality of predefined holding styles, such as a front holdingstyle or a pocket holding style. To detect such a holding style, themobile communication apparatus may include a camera, as a smartphonedoes. The front holding style may be determined when the camera capturesan image of the face of the pedestrian. When an acceleration sensor isemployed to successively detect the amount of movement of the mobilecommunication apparatus relative to the position of such a front holdingstyle, the holding style for the mobile communication apparatus can bedetected. A simpler alternative is to attach a display to the mobilecommunication apparatus, designate the holding style to be employed bythe pedestrian, and instruct the pedestrian to press a button when thedesignated holding style is employed.

<Fourth Modification>

In the foregoing embodiments, the reference signal R is transmitted todetermine the propagation path characteristics information CC. However,the transmission of the reference signal R is not essential to determinethe propagation path characteristics information CC. The referencesignal R is a signal known by the receiving end. However, if thereceiving end returns a reception status to the transmitting end, thetransmitting end can determine the propagation path characteristicsinformation CC from the returned reception status and a signaltransmitted from the transmitting end because the transmitted signal isknown to the transmitting end. This instance may use any signal fordetermining the propagation path characteristics information CC,providing an advantage in eliminating overhead introduced by adding thereference signal R.

<Fifth Modification>

The radio wave propagation map 221 may be stored by a server capable ofcommunicating with the base station 200.

<Sixth Modification>

In the first embodiment, the model of the in-vehicle terminal 300 isregarded as the antenna determination information, and the radio wavepropagation map 221 used by the propagation path characteristicsacquirer section 234 to acquire the propagation path characteristicsinformation CC is the same as for the model of the in-vehicle terminal300, which is included in the position prediction information. Thereason is that the antenna characteristics remain unchanged when thesame model is employed. Alternatively, information other than the modelof the in-vehicle terminal 300 may be used to determine whether the sameantenna characteristics are exhibited. The degree of similarityregarding the antenna characteristics as being the same is determineddepending on performance requirements.

A sixth modification uses antenna determination information other thanthe model of the in-vehicle terminal 300. Specifically, the antennadetermination information uses the model name of the vehicle 4, whichmay be referred to as the vehicle name. As far as being attached to thevehicle 4 prior to its shipment, the model of the in-vehicle terminal300 can be identified by determining the model name of the vehicle 4;thus, the model name of the vehicle 4 can be used as the antennadetermination information. As classifying the vehicle 4, the model nameof the vehicle 4 corresponds to an example of a vehicle classification.

In the sixth modification, the characteristics determination informationuploader section 335 and position prediction information uploadersection 336 of the in-vehicle terminal 300 upload the model name of thevehicle 4 instead of the model of the in-vehicle terminal 300. To uploadthe model name of the vehicle 4, the storage unit 320 of the in-vehicleterminal 300 stores the model name of the vehicle 4 in advance.

The radio wave propagation map 221 stored in the base station 200 iscreated by preparing the propagation path characteristics information CCfor each model name of the vehicle 4. Based on the model name of thevehicle 4, the map adjuster section 231 identifies the radio wavepropagation map 221 to be updated. The radio wave propagation map 221used by the propagation path characteristics acquirer section 234 toacquire the propagation path characteristics information CC is the sameas for the model name of the vehicle 4 that is included in the positionprediction information.

<Seventh Modification>

A seventh modification uses a vehicle type classification as the antennadetermination information. The vehicle type classification is performedby classifying the types of vehicles according to similarity of antennacharacteristics. When the model name of the vehicle 4 described inconjunction with the sixth modification is used as the antennadetermination information, the same antenna characteristics areconsidered to be exhibited as far as the same model name of the vehicle4 is encountered. This provides an advantage enabling a resourceselection based on the propagation path characteristics information CChaving the same antenna characteristics as the selected resourceantenna. However, the radio wave propagation map 221 needs to beprepared for each model name of the vehicle 4.

The vehicle type classification is performed to provide higherversatility of the radio wave propagation map 221 than the model name ofthe vehicle 4. A range within which the antenna characteristics remainunchanged is regarded as one classification. Thus, the vehicle typeclassification relates to a concept wider than the model name of thevehicle 4 that is described in conjunction with the sixth modification.Meanwhile, when vehicles are broadly classified, a concept such as anautomobile or a railroad vehicle is encountered. These classificationsare based on a social infrastructure on which the vehicles travel.However, the vehicle type classification performed here relates to aconcept narrower than an automobile and a railroad vehicle.Specifically, the vehicle type classification may be a passenger car ora bus under the automobile, or a bullet train under the railroadvehicle. The vehicle type classification may be performed according tothe overall height of a vehicle. The vehicle type classificationprovides the classification of vehicles and thus corresponds to anexample of a vehicle classification.

In the seventh modification, the characteristics determinationinformation uploader section 335 and position prediction informationuploader section 336 of the in-vehicle terminal 300 upload the vehicleclassification instead of the model of the in-vehicle terminal 300. Toupload the vehicle type classification, the storage unit 320 of thein-vehicle terminal 300 stores the vehicle type classification inadvance.

The radio wave propagation map 221 stored in the base station 200 iscreated by preparing the propagation path characteristics information CCfor each vehicle type classification. Based on the vehicle typeclassification, the map adjuster section 231 identifies the radio wavepropagation map 221 to be updated. The radio wave propagation map 221used by the propagation path characteristics acquirer section 234 toacquire the propagation path characteristics information CC is the sameas for the vehicle type classification included in the positionprediction information.

<Eighth Modification>

An eighth modification uses the mounting height of the antenna as theantenna determination information. The propagation path characteristicsvary with the three-dimensional position. Therefore, the mounting heightof the antenna is also applicable as an antenna characteristic.

In the eighth modification, the characteristics determinationinformation uploader section 335 and position prediction informationuploader section 336 of the in-vehicle terminal 300 upload the mountingheight of the antenna 313, that is, the antenna determinationinformation including the mounting height of the selected resourceantenna, instead of the model of the in-vehicle terminal 300. Themounting height of the antenna 313 is stored beforehand in the storageunit 320. The antenna determination information to be uploaded mayinclude the antenna format and the antenna posture in addition to themounting height of the selected resource antenna.

The radio wave propagation map 221 stored in the base station 200 iscreated by preparing the propagation path characteristics information CCfor each reference antenna classified according to the aforementionedantenna determination information. Namely, the radio wave propagationmap 221 is created by preparing the propagation path characteristicsinformation CC for each mounting height of the reference antenna and foreach antenna format and other antenna determination information.

Based on the position of reception of the reference signal R and thepropagation path characteristics information CC, which are uploadedtogether with the antenna determination information by thecharacteristics determination information uploader section 335, the mapadjuster section 231 updates the radio wave propagation map 221 for thereference antenna that is equal to the antenna 313 in the mountingheight and other antenna characteristics.

The radio wave propagation map 221 used by the propagation pathcharacteristics acquirer section 234 to acquire the propagation pathcharacteristics information CC is determined by antenna determinationinformation other than the antenna mounting height included in theposition prediction information and in compliance with a mounting heightcondition.

The mounting height condition is that the difference or ratio betweenthe mounting height of the antenna 313, which is included in theposition prediction information, and the mounting height of thereference antenna is within a predetermined range. If two or morereference antennas comply with the condition, the radio wave propagationmap 221 for a reference antenna having a mounting height closest to themounting height of the antenna 313 is used to acquire the propagationpath characteristics information CC.

Even when vehicles differ in vehicle model, the eighth modification canapply the same radio wave propagation map 221 to the vehicles as far asthey are equal in antenna mounting height and other antennacharacteristics. For example, a station wagon car having a relativelysmall overall height and a sedan car having a relatively great overallheight are different in vehicle model, but their antenna mountingheights may comply with the aforementioned mounting height condition.Further, the eighth modification can apply radio wave propagation maps221 for different antenna mounting heights to vehicles having a vehicleheight adjustment function even when the vehicles are equal in vehiclemodel.

<Ninth Modification>

A ninth modification uses a holding style for the antenna 313 as theantenna determination information. Specifically, the holding styleindicates whether the antenna is securely fixed. When the antenna is notsecurely fixed, a mobile terminal is used as the mobile communicationapparatus and is not attached to a holder secured to the mobile object.Whether the mobile terminal is attached to the holder secured to themobile object is determined based on the acceleration detected by anacceleration sensor incorporated in the mobile terminal. When the mobileterminal is moved without being attached to the holder secured to themobile object, the acceleration detected by the acceleration sensorexhibits more complicated temporal changes than when the mobile terminalis attached to the holder. Thus, whether the mobile terminal is attachedto the holder is determined based on the temporal changes in theacceleration. Further, when the mobile terminal is not attached to theholder secured to the mobile object, the position of the mobile terminalexhibits more complicated temporal changes than when the mobile terminalis attached to the holder. Thus, whether the mobile terminal is attachedto the holder may be determined based on the temporal changes in theposition.

In the ninth modification, the characteristics determination informationuploader section 335 and position prediction information uploadersection 336 of the mobile communication apparatus upload informationindicative of whether the mobile communication apparatus is secured, asthe antenna determination information, instead of the model of thein-vehicle terminal 300. The storage unit 320 of the mobilecommunication apparatus stores information indicative of whether themobile communication apparatus is of a fixed type or of a portable type.If the mobile communication apparatus is of a fixed type, it is assumedthat the mobile communication apparatus is secured. Meanwhile, if themobile communication apparatus is a mobile terminal, whether the mobilecommunication apparatus is attached to the holder secured to the mobileobject is determined based on temporal changes in the acceleration ofposition.

Further, the mobile communication apparatus of a fixed type alsouploads, as the holding style, information indicative of a securing partto which the mobile communication apparatus is secured. Securing partsare also stored in the storage unit 320. The securing parts aredifferentiated from each other depending on whether the antennacharacteristics vary. The securing parts stored in memory are, forexample, a rooftop, a mirror, a window, and a trunk grid.

Meanwhile, if the mobile communication apparatus is of a portable type,whether the mobile communication apparatus is used in a mobile objecthaving a plurality of seats is determined. If it can be determined thatthe mobile communication apparatus is used in a mobile object having aplurality of seats, which seat is the place of the mobile communicationapparatus is also determined.

Further, information indicative of whether the mobile communicationapparatus is used in a mobile object having a plurality of seats andinformation indicative of a seat in which the mobile communicationapparatus is used are additionally uploaded as the holding style.Whether the mobile communication apparatus is used in a mobile objecthaving a plurality of seats and which seat is the place of the mobilecommunication apparatus are determined based on inquiries to a userholding the mobile communication apparatus.

The radio wave propagation map 221 stored in the base station 200 iscreated by preparing the propagation path characteristics information CCthat varies depending on whether the mobile communication apparatus isof a fixed type or of a portable type. Further, for the mobilecommunication apparatus of a fixed type, the propagation pathcharacteristics information CC on each of the aforementioned securingparts is prepared. Meanwhile, for the mobile communication apparatus ofa portable type, the radio wave propagation map 221 is created variouslydepending on whether the mobile communication apparatus is used in amobile object having a plurality of seats. Further, the radio wavepropagation map 221 for the mobile communication apparatus used in amobile object having a plurality of seats is created for each seat wherethe mobile communication apparatus is used.

The map adjuster section 231 updates the radio wave propagation map 221that is equal in holding style to the antenna determination information.Further, the radio wave propagation map 221 used by the propagation pathcharacteristics acquirer section 234 to acquire the propagation pathcharacteristics information CC is equal in holding style to the antennadetermination information.

<Tenth Modification>

In the eighth modification, the antenna type may also be used as theantenna determination information in addition to the antenna mountingheight. Further, in the ninth modification, the antenna type may also beused as the antenna determination information in addition to the holdingstyle.

While the present disclosure has been described with reference toembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. The present disclosure isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the spirit and scope of the present disclosure.

What is claimed is:
 1. A mobile communication system including (i) a mobile communication apparatus used in a mobile object and (ii) a target communication apparatus that is a target with which the mobile communication apparatus communicates, the mobile communication apparatus including a selected resource antenna permitting communication using a selected resource, the mobile communication apparatus establishing wireless communication using the selected resource antenna, the mobile communication system comprising: a propagation path characteristics acquirer section that acquires propagation path characteristics information in association with a future communication position, the propagation path characteristics information being information about propagation path characteristics between (i) the target communication apparatus and (ii) a reference antenna that is equal to the selected resource antenna in antenna characteristics, the antenna characteristics including at least an antenna format; and a resource selector section that, based on the propagation path characteristics information acquired by the propagation path characteristics acquirer section, selects in advance a resource used in communication at the future communication position between the mobile communication apparatus and the target communication apparatus before the selected resource antenna of the mobile communication apparatus comes to be placed at the future communication position.
 2. The mobile communication system according to claim 1, further comprising: a position prediction information acquirer section that acquires position prediction information to predict a position of the selected resource antenna of the mobile communication apparatus; and a position predictor section that successively determines a predicted position of the selected resource antenna based on the position prediction information, wherein: the propagation path characteristics acquirer section acquires the propagation path characteristics information at the predicted position from a radio wave propagation map that is a database storing the propagation path characteristics information in association with the future communication position; and the resource selector section regards the predicted position as the future communication position and selects a resource used in communication at the predicted position between the mobile communication apparatus and the target communication apparatus.
 3. The mobile communication system according to claim 2, wherein: the target communication apparatus is a base station; the base station includes the position prediction information acquirer section, the position predictor section, the propagation path characteristics acquirer section, the resource selector section, and a storage unit storing the radio wave propagation map; the radio wave propagation map stores the propagation path characteristics information about a plurality of different types of the reference antenna; the mobile communication apparatus includes a position prediction information uploader section that uploads, to the base station, (i) the position prediction information when and after uploading and (ii) antenna determination information used to determine the antenna characteristics; and the propagation path characteristics acquirer section in the base station regards the predicted position predicted by the position predictor section as the future communication position, determines the reference antenna based on the antenna determination information uploaded from the mobile communication apparatus, and acquires from the radio wave propagation map the propagation path characteristics information dependent on the predicted position and the determined reference antenna.
 4. The mobile communication system according to claim 3, wherein: the mobile object is a vehicle; the position prediction information uploader section in the vehicle uploads a vehicle classification as the antenna determination information, the vehicle classification being obtained by classifying the vehicle according to the antenna characteristics exhibited when the mobile communication apparatus is used in the vehicle; and the propagation path characteristics acquirer section in the base station determines the reference antenna based on the vehicle classification.
 5. The mobile communication system according to claim 4, wherein: the position prediction information uploader section in the vehicle uploads a model name of the vehicle as the vehicle classification; and the propagation path characteristics acquirer section in the base station determines the reference antenna based on the model name of the vehicle.
 6. The mobile communication system according to claim 4, wherein: the position prediction information uploader section in the vehicle uploads a vehicle type classification as the vehicle classification, the vehicle type classification being obtained by classifying a type of the vehicle according to similarity of the antenna characteristics; and the propagation path characteristics acquirer section in the base station determines the reference antenna based on the vehicle type classification.
 7. The mobile communication system according to claim 3, wherein: the mobile object is a vehicle; the position prediction information uploader section in the vehicle uploads a mounting height of the selected resource antenna when the mobile communication apparatus is used in the vehicle; and the propagation path characteristics acquirer section in the base station determines the reference antenna based on (i) the mounting height of the selected resource antenna and (ii) the mounting height of the reference antenna.
 8. The mobile communication system according to claim 3, wherein: the position prediction information uploader section uploads a holding style of the selected resource antenna as the antenna determination information; and the propagation path characteristics acquirer section in the base station determines the reference antenna based on whether the selected resource antenna is equal to the reference antenna in holding style.
 9. The mobile communication system according to claim 8, wherein when determining whether the selected resource antenna is equal to the reference antenna in holding style, the propagation path characteristics acquirer section in the base station determines based on whether the selected resource antenna and the reference antenna are both secured.
 10. The mobile communication system according to claim 9, wherein, when determining whether the selected resource antenna is equal to the reference antenna in holding style, the propagation path characteristics acquirer section in the base station determines based on whether each of the selected resource antenna and the reference antenna is secured to an identical securing part as well as whether the selected resource antenna and the reference antenna are both secured.
 11. The mobile communication system according to claim 8, wherein, when the selected resource antenna and the reference antenna are both unsecured, the propagation path characteristics acquirer section in the base station determines whether the selected resource antenna is equal to the reference antenna in holding style based on whether each of the selected resource antenna and the reference antenna is placed in an identical seat.
 12. The mobile communication system according to claim 3, wherein: the mobile communication apparatus includes the reference antenna, a position determiner section that successively determines a current position, and a characteristics determination information uploader section that uploads (i) characteristics determination information and (ii) an uploading-time position to the base station, the characteristics determination information being either the propagation path characteristics information or information determining the propagation path characteristics information, the uploading-time position being a current position most lately determined by the position determiner section; and the base station includes a map adjuster section that updates the radio wave propagation map based on the characteristics determination information and the uploading-time position, which are uploaded by the mobile communication apparatus.
 13. The mobile communication system according to claim 12, wherein: the radio wave propagation map in the base station includes a reliability index indicative of reliability of the propagation path characteristics information included in the radio wave propagation map; and the resource selector section in the base station selects a resource by using the propagation path characteristics information and the reliability index related to the propagation path characteristics.
 14. The mobile communication system according to claim 13, wherein the reliability index is a reproducibility index indicative of reproducibility of the propagation path characteristics information, the reproducibility index being determined based on a plurality of the propagation path characteristics informations on positions each identical to the future communication position.
 15. The mobile communication system according to claim 13, wherein: the mobile communication apparatus includes an error detector section that, upon receipt of a signal transmitted from the base station, detects an error in the received signal, and an error resource uploader section that uploads error resource information to the base station, the error resource information being indicative of a resource used to transmission of the signal having the error detected by the error detector section; and the base station includes a reliability adjuster section that updates the reliability index based on the error resource information.
 16. The mobile communication system according to claim 12, wherein: the mobile communication apparatus includes a download data storage unit that stores the radio wave propagation map downloaded from an outside source, a characteristics information determiner section that determines the propagation path characteristics information, when the reference antenna receives a signal transmitted from the base station, and a difference determiner section that determines a propagation path characteristics difference, the propagation path characteristics difference being a difference between the propagation path characteristics information determined by the characteristics information determiner section and a portion of the radio wave propagation map stored in the download data storage unit, the portion corresponding to the propagation path characteristics information determined by the characteristics information determiner section; the characteristics determination information uploader section uploads the propagation path characteristics difference as the characteristics determination information; and the map adjuster section in the base station updates the radio wave propagation map based on the propagation path characteristics difference.
 17. The mobile communication system according to claim 12, further comprising: a distance determiner section that acquires a movement speed of the mobile communication apparatus and determines a movement distance during a communication period from the acquired movement speed; a characteristics change determiner section that determines a change in the propagation path characteristics information during the communication period based on (i) the movement distance determined by the distance determiner section and (ii) the radio wave propagation map; and a characteristics change compensator section that applies compensation to a communication signal so as to reduce an influence upon communication due to the change in the propagation path characteristics information during the communication period, the change being determined by the characteristics change determiner section.
 18. The mobile communication system according to claim 1, wherein: the target communication apparatus successively transmits a propagation path estimation signal; the mobile communication apparatus includes a front antenna and a rear antenna and uses the front antenna as the reference antenna and the rear antenna as the selected resource antenna, the front antenna and the rear antenna each being of an identical format and longitudinally disposed in a travel direction of the mobile object; the mobile communication apparatus further includes a characteristics information determiner section that determines front antenna propagation path characteristics information, the front antenna propagation path characteristics information being the propagation path characteristics information obtained when the propagation path estimation signal transmitted from the target communication apparatus is received by the front antenna at a front-antenna receiving position that is a position where the propagation path estimation signal transmitted is received by the front antenna, and a reception information transmitter section that transmits to the target communication apparatus a movement speed of the mobile communication apparatus and the front antenna propagation path characteristics information that are obtained when the propagation path estimation signal is received by the front antenna; the target communication apparatus includes the propagation path characteristics acquirer section and the resource selector section; the propagation path characteristics acquirer section acquiring the front antenna propagation path characteristics information transmitted from the mobile communication apparatus in association with a position where the front antenna propagation path characteristics information is received by a receiver in the target communication apparatus, the resource selector section regards as the future communication position the front-antenna receiving position where the propagation path estimation signal is received by the front antenna in the mobile communication apparatus, the resource selector section selecting a resource used in communication at the front-antenna receiving position; and the target communication apparatus further includes a timing determiner section that determines a rear communication time based on the movement speed transmitted from the mobile communication apparatus, the rear communication time being a time at which the rear antenna comes to be placed at the front-antenna receiving position where the propagation path estimation signal was communicated by the front antenna, and a communication controller section that communicates with the mobile communication apparatus by using a resource selected by the resource selector section at the rear communication time determined by the timing determiner section.
 19. The mobile communication system according to claim 18, wherein: a time at which the propagation path estimation signal used by the timing determiner section to determine the rear communication time is transmitted from the target communication apparatus is regarded as a front communication time; the communication controller section of the target communication apparatus transmits the propagation path estimation signal at the rear communication time; the characteristics information determiner section of the mobile communication apparatus determines rear antenna propagation path characteristics information in addition to the front antenna propagation path characteristics information, the rear antenna propagation path characteristics information being the propagation path characteristics information obtained when the propagation path estimation signal is transmitted from the target communication apparatus at the rear communication time; the reception information transmitter section of the mobile communication apparatus transmits (i) a current position where the propagation path estimation signal is received at the front communication time and (ii) the rear antenna propagation path characteristics information, to the target communication apparatus, in addition to the movement speed of the mobile communication apparatus and the front antenna propagation path characteristics information that are obtained when the propagation path estimation signal is received at the front-time communication time; the target communication apparatus further includes a reproducibility index database that associates a spot with a reproducibility index indicative of reproducibility of the propagation path characteristics information, and a reproducibility determiner section that determines, based on a comparison between the front antenna propagation path characteristics information and the rear antenna propagation path characteristics information, the reproducibility index with respect to a spot associated with the front antenna propagation path characteristics information, and updates the reproducibility index database based on the determined reproducibility index; and the communication controller section of the target communication apparatus determines, based on (i) a current position received together with the front antenna propagation path characteristics information and (ii) the reproducibility index database, a parameter setting on the reliability of communication at transmitting the propagation path estimation signal at the rear communication time.
 20. The mobile communication system according to claim 1, wherein: the target communication apparatus is mounted in a first mobile object different from the mobile object using the mobile communication apparatus, the mobile object using the mobile communication apparatus being regarded as a second mobile object; the mobile communication apparatus includes a front antenna and a rear antenna, uses the front antenna as the reference antenna and the rear antenna as the selected resource antenna, and transmits a movement speed of the second mobile object and a propagation path estimation signal from the front antenna, the front antenna and the rear antenna each being of an identical format and longitudinally disposed in a travel direction of the second mobile object; the target communication apparatus includes (i) the propagation path characteristics acquirer section and the resource selector section; the target communication apparatus further includes a target-apparatus front antenna and a target-apparatus rear antenna, the target-apparatus front antenna and the target-apparatus rear antenna each being of an identical format and longitudinally disposed in a travel direction of the first mobile object, and a characteristics information determiner section that, when the target-apparatus front antenna receives the propagation path estimation signal and the movement speed at a subject time, regards a subject position of the front antenna of the mobile communication apparatus at a time when the propagation path estimation signal is transmitted from the mobile communication apparatus, as the future communication position, determines the propagation path characteristics information based on the received propagation path estimation signal, and stores the determined propagation path characteristics information in a predetermined storage unit; the propagation path characteristics acquirer section in the target communication apparatus acquires the propagation path characteristics information on the future communication position from the predetermined storage unit; and the target communication apparatus further includes a timing determiner section that determines, based on the movement speed received by the target-apparatus front antenna, a time at which the rear antenna of the mobile communication apparatus comes to be placed at the subject position where the propagation path estimation signal is transmitted from the front antenna of the mobile communication apparatus, and a communication controller section that, at the time determined by the timing determiner section, communicates with the rear antenna of the mobile communication apparatus by using a resource selected by the resource selector section from either the target-apparatus front antenna or the target-apparatus rear antenna, whichever is closer to a position of the target-apparatus front antenna at the subject time of receiving the propagation path estimation signal.
 21. The mobile communication system according to claim 1, wherein the mobile communication apparatus includes a plurality of antenna elements, the antenna elements each being of an identical antenna format and disposed with intervals, and a communication controller section that selects two antenna element groups each having antenna elements disposed in an identical pattern, the two antenna element groups including two or more of the antenna elements and being longitudinally disposed in a travel direction of the mobile object, and establishes communication by using a front one group among the two selected antenna element groups as a front antenna acting as the reference antenna and a rear one group among the two selected antenna element group as a rear antenna acting as the reference antenna.
 22. The mobile communication system according to claim 21, wherein: the target communication apparatus successively transmits a propagation path estimation signal; the mobile communication apparatus includes a characteristics information determiner section that determines front antenna propagation path characteristics information with respect to each combination between (i) an antenna used by the target communication apparatus to transmit the propagation path estimation signal and (ii) the antenna elements forming the front antenna, the front antenna propagation path characteristics information being the propagation path characteristics information obtained when the propagation path estimation signal transmitted from the target communication apparatus is received by the antenna elements forming the front antenna, and a reception status signal transmitter section that transmits, to the target communication apparatus, (i) a movement speed of the mobile communication apparatus at a time of reception of the propagation path estimation signal by the front antenna, (ii) the front antenna propagation path characteristics information determined by the characteristics information determiner section, and (iii) an inter-antenna distance being a distance between corresponding antenna elements of the front antenna and the rear antenna; the target communication apparatus includes the propagation path characteristics acquirer section and the resource selector section, the propagation path characteristics acquirer section acquiring the front antenna propagation path characteristics information transmitted from the mobile communication apparatus from a receiver in the target communication apparatus in association with a reception position, the resource selector section selecting a resource used in communication at a front-antenna receiving position where the propagation path estimation signal is received by the front antenna, the front-antenna receiving position being regarded as the future communication position; and the target communication apparatus further includes a timing determiner section that determines a rear communication time based on the movement speed and the inter-antenna distance received from the mobile communication apparatus, the rear communication time being a time at which the rear antenna comes to be placed at the front-antenna receiving position where the propagation path estimation signal is received by the front antenna, and a communication controller section that communicates with the mobile communication apparatus by using a resource selected by the resource selector section at the rear communication time determined by the timing determiner section.
 23. The mobile communication system according to claim 22, wherein: the communication controller section in the target communication apparatus transmits the propagation path estimation signal at the rear communication time; the characteristics information determiner section in the mobile communication apparatus determines rear antenna propagation path characteristics information with respect to each combination between (i) an antenna used by the target communication apparatus to transmit the propagation path estimation signal and (ii) the antenna elements forming the rear antenna, the rear antenna propagation path characteristics information being the propagation path characteristics information obtained when the propagation path estimation signal transmitted from the target communication apparatus at the rear communication time is received by the rear antenna; the reception status signal transmitter section in the mobile communication apparatus transmits the rear antenna propagation path characteristics information to the target communication apparatus; the target communication apparatus includes a reproducibility determiner section that determines a reproducibility index indicative of reproducibility of the propagation path characteristics information on the future communication position by comparing the front antenna propagation path characteristics information and the rear antenna propagation path characteristics information with each other in respect of each corresponding combination of antenna elements of the front antenna and antenna elements of the rear antenna; and the resource selector section selects a resource used in communication at the future communication position based on (i) the propagation path characteristics information acquired by the propagation path characteristics acquirer section and (ii) the reproducibility index determined by the reproducibility determiner section.
 24. The mobile communication system according to claim 22, wherein, based on (i) a transmission cycle in which the target communication apparatus transmits a signal and (ii) the movement speed of the mobile communication apparatus that is received by the receiver of the target communication apparatus, the mobile communication apparatus allocates the antenna elements to the front antenna and the rear antenna such that the inter-antenna distance is equal to or greater than a distance moved by the mobile communication apparatus during one transmission cycle.
 25. A communication apparatus to communicate with a mobile communication apparatus used in a mobile object, the mobile communication apparatus having a selected resource antenna permitting communication using a selected resource, the communication apparatus comprising: a propagation path characteristics acquirer section that acquires propagation path characteristics information in association with a future communication position, the propagation path characteristics information being information about propagation path characteristics between the communication apparatus and a reference antenna that is equal to the selected resource antenna in antenna characteristics including at least an antenna format; and a resource selector section that selects in advance, based on the propagation path characteristics information acquired by the propagation path characteristics acquirer section, a resource used in communication at the future communication position between the mobile communication apparatus and the communication apparatus before the selected resource antenna of the mobile communication apparatus comes to be placed at the future communication position. 